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“Could not start transfer” is a queue status, not a diagnosis. FileZilla has already failed to open, read, write, or negotiate the transfer, but the useful reason is usually in the log lines immediately before that message. Expand the failed item, copy the complete log, and identify whether the operation was an upload or download before changing settings. Then check the local file, remote permissions, and FTP data connection in that order.
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What “Could Not Start Transfer” Means
FileZilla uses the phrase “Could not start transfer” as a general failed-transfer result in the queue. It does not tell you whether the problem is a missing local file, a protected folder, a server permission, a blocked data port, or a connection that timed out. The status is therefore the end of the investigation, not the explanation.
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The first explicit error normally appears earlier in the message log. A support example shows the queue status alongside a local file-open or read failure. That distinction matters: changing passive mode cannot repair a source file that no longer exists, and changing folder permissions cannot repair a firewall that blocks the data connection.
Before retrying, record four facts:
- Whether you were uploading from your computer or downloading to it.
- The complete local path, including the drive or mount point.
- The remote path and the account used to connect.
- The first specific error before the queue summary, rather than the final queue wording.
Do not diagnose from the queue pane alone. If the log is collapsed, expand the transfer details or copy the session log into a text file so that a later retry does not overwrite the evidence.
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- Stop repeated retries. Repeated attempts can produce a long queue and hide the original error. Pause the queue and select one failed file.
- Classify the direction. For an upload, FileZilla must read the local source and the server must accept a write. For a download, the server must permit a read and your computer must create or overwrite the local destination.
- Check the two paths manually. Open the local folder in your operating system and verify the remote directory in FileZilla. A renamed, moved, disconnected, or case-sensitive path can fail before networking is involved.
- Try one small test file. Use a harmless file in a directory you know is permitted. A tiny successful transfer points toward a file-specific, size-related, or long-connection problem rather than a total login failure.
- Separate login from transfer. A successful username and password prove only that the control connection and authentication worked. Directory listing and file movement use a second data connection and can fail independently.
Keep the original log with the test result. It gives a hosting provider or server administrator something actionable instead of a generic “FileZilla failed” report.
Check the Local File and Destination
For uploads: verify that FileZilla can read the source
- Confirm that the file still exists at the exact path shown in the transfer log. Cloud-sync placeholders, removable drives, and network mounts may display a filename while the content is unavailable.
- Open the file or copy it to a normal local folder to test readability. If the operating system reports an I/O error, repair the storage or obtain a fresh copy before troubleshooting FTP.
- Close applications that may hold an exclusive lock, such as an editor exporting the same file, a database process, or a backup utility. Retry after the writing program has finished and released the file.
- Move a test copy out of protected system folders. Operating-system permissions can prevent FileZilla from reading a source even though the file is visible in a file manager.
- Check the filename and complete path for characters, excessive length, or a disconnected drive letter. Test with a short name such as
transfer-test.txtin a user-owned folder.
For downloads: verify that FileZilla can write the destination
- Make sure the destination folder still exists and is on a mounted, writable disk.
- Check free space, especially when a partial file already occupies the name. A full volume can make a transfer fail at its first write.
- Close a program that has the destination file open or locked. If overwriting is not required, choose a new filename and test again.
- Use a folder where your operating-system account normally has write access rather than a protected system directory.
- Confirm that security software is not quarantining or immediately removing the newly created file. Its event log can show a block that FileZilla itself cannot explain.
If a local copy operation fails outside FileZilla, fix that local problem first. FTP settings cannot grant your desktop application permission to read or write a path that the operating system denies.
Check the Remote Directory, Account, and Quota
Remote permissions are separate from local permissions. An account may log in successfully but be restricted to a specific home directory, a read-only folder, or a limited set of operations.
Confirm the remote path
Look at the current remote directory shown in FileZilla before starting the transfer. Some servers present a virtual path that differs from the filesystem path used by an administrator. Navigate to a directory you know is part of the account’s home area, then retry a small file. A path copied from a web control panel may not be valid in FTP, and a directory can be case-sensitive even when your local system is not.
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Match the permission to the operation
- An upload needs permission to create or replace a file in the destination directory.
- A download needs permission to read the remote file and, where applicable, list or traverse its parent directories.
- Replacing an existing file can require a different server policy from creating a new one.
- Some accounts are restricted by a quota, a storage limit, an expired subscription, an IP policy, or a chroot-style home directory.
If a test succeeds in one remote folder but fails in another, the difference is almost certainly the remote path or its policy, not FileZilla’s transfer engine. Protected directories, server-side locks, quotas, and account rules must be changed by the server administrator or hosting provider. Send that administrator the exact remote path, account name (never the password), operation, timestamp, and complete log.
Why Login Can Work While Transfers Fail
FTP uses at least two connections. The control connection carries commands such as login, directory changes, and transfer requests. A separate data connection carries the directory listing or file contents. The control connection commonly reaches the server on the FTP service port, while the data connection uses a negotiated port.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsThis architecture explains a common pattern: FileZilla connects and authenticates, but a directory listing hangs or a transfer ends with “Could not start transfer.” A firewall, antivirus product, NAT router, or server passive-port configuration may allow the control connection while blocking the data channel.
Passive mode is the normal starting point for a client behind a home router or firewall. FileZilla’s official network guidance describes it this way: in passive mode, the client sends the PASV command and the server responds with an address. The client then opens the data connection outward, which generally fits networks that block unsolicited inbound connections.
Passive and Active FTP Modes Compared
| Characteristic | Passive mode | Active mode |
|---|---|---|
| Who opens the data connection? | The client opens an outgoing connection to the server-provided address and port. | The server connects back to the client for the data channel. |
| Typical fit | Clients behind NAT, home routers, and restrictive inbound firewalls. | Networks where the client can accept the server’s callback connection. |
| Main configuration concern | The server must advertise reachable passive addresses and permit its passive port range. | The client must advertise the correct external address and expose or forward an appropriate port range. |
| Firewall sensitivity | Usually simpler for the client because connections are outbound, but server-side ports still must be reachable. | More sensitive to client firewalls, NAT, and incorrect port forwarding. |
| First choice for troubleshooting | Yes, unless the server operator specifically requires active mode. | Use only when passive mode is incompatible or the server requires it. |
Switching modes is not a universal cure. If the local source is unreadable or the account lacks permission, both modes fail. Mode changes are useful when the log indicates that the data connection cannot be opened, the directory listing times out, or the server returns a connection-direction error.
Set Passive Mode and Run FileZilla’s Network Wizard
FileZilla’s official guidance recommends running the Network Configuration Wizard when network behavior is uncertain. Menu names can vary slightly by release, but the relevant controls are in the network configuration area and in the site’s transfer settings.
- Open Edit and choose Network Configuration Wizard (or the similarly named network wizard in your build).
- Let the wizard test the connection. Record whether it reports that passive transfers work, whether an external address is detected, and which ports are being tested.
- In the site connection settings, open Transfer Settings and select Passive or Default transfer mode. Use an explicit passive setting while diagnosing so the behavior is unambiguous.
- Reconnect, request a directory listing, and then try one small upload or download. A successful listing followed by a failed file transfer points to permissions or the particular file; a failed listing still points to the data connection.
- If the wizard identifies a firewall or router issue, make the smallest change it recommends, then test again. Do not open broad inbound port ranges or disable security software permanently.
Passive mode may use server-selected ports rather than the control port. Therefore, opening only the familiar FTP service port on a firewall is not necessarily sufficient. The server operator must configure and expose a passive-port range, and the client network must allow the resulting outbound connection.
Review Firewalls, Antivirus, and NAT
On the computer running FileZilla
- Confirm that FileZilla is allowed to make outgoing network connections on the network profile you are using.
- Review the firewall and antivirus event logs at the exact time of the failed attempt. A blocked executable, inspection rule, or ransomware-protection feature can prevent file access or the data connection.
- Test with security software temporarily placed in its documented audit or exception mode only if your organization permits it, then restore protection immediately after the test. A successful test identifies the control that needs a narrow allow rule; it is not a reason to leave protection disabled.
- Check whether a VPN, proxy, or endpoint security agent changes the route or filters FTP commands. Test one variable at a time so that the log remains interpretable.
On the router or NAT gateway
Passive mode normally avoids inbound connections to the client, but the router still has to permit the outbound data session and keep its connection-tracking entry alive. Active mode requires the server to reach the client’s advertised external address and forwarded port range; an address belonging to the private LAN will not work from the public internet.
If the same account works from a different trusted network, your local firewall, NAT device, ISP filtering, or corporate policy becomes more likely. Only perform that comparison when transferring the data is appropriate for the network and the account. Never move confidential files to an untrusted network merely as a test.
FTP Over TLS Versus Plain FTP
| Option | What it protects | Compatibility consideration | When to use |
|---|---|---|---|
| FTP over TLS | Encrypts credentials and, when negotiated for the data channel, the transferred content. | Requires the server to support TLS and present a certificate configuration that the client can negotiate. | Preferred whenever the server offers it. |
| Plain FTP | Does not protect usernames, passwords, commands, or file contents from network observers. | May work with legacy servers that cannot negotiate TLS. | Only when the server operator confirms that compatibility requires it and the risk is accepted. |
A TLS negotiation failure is different from a blocked data connection. Read the first explicit log message: certificate or handshake text points to encryption compatibility; a timeout after login points more toward the data path. Do not switch to plain FTP simply because a transfer failed. If a fallback is unavoidable, use it only on a network and for data where the server operator has assessed the exposure.
Large Transfers That Fail Near the End
During a file transfer, the data channel carries the content while the control channel may remain quiet. Some routers and firewalls drop an apparently idle control connection even though bytes are still moving on the data channel. The result can be a large file that works for several minutes and then ends with a generic transfer failure, while small files succeed.
- Compare a small file with a file that takes substantially longer, and note the elapsed time at failure.
- Prevent the computer from sleeping and keep the network link active for the test.
- Check router, firewall, and endpoint-security logs for an idle-session timeout or reset at the failure time.
- Ask the server administrator whether its passive ports, connection limits, or maximum transfer duration are configured for long sessions.
- If the server supports resuming and the log confirms an interrupted data channel, resume only after verifying that the partial destination is the correct file. Otherwise, remove the partial file and make a clean retry.
Do not infer a timeout solely from the file size. A slow link, a server quota, storage exhaustion, or a security scan can produce the same symptom; the timing and log wording distinguish them.
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Use the Log to Choose the Correct Branch
| What you observe | Most useful next check |
|---|---|
| The log says the local file cannot be opened or read. | Verify existence, locks, protected-folder access, drive availability, and local readability. Test a copy in a user-owned folder. |
| The remote listing works, but an upload is rejected. | Check the account’s write/create permission, destination path, quota, and whether replacing an existing file is restricted. |
| The remote listing works, but a download is rejected. | Check remote read permission, the local destination’s write access, free space, and file locks. |
| Login succeeds but listing and transfers both time out. | Use passive mode, run the network wizard, and inspect client/server firewall and passive-port configuration. |
| Small files work and long files fail. | Investigate idle connection timeouts, sleep settings, router state tracking, server limits, and long-running security scans. |
| The failure occurs only in one remote directory. | Treat it as a path or server-policy issue and ask the administrator to verify permissions and quota for that directory. |
This table is a routing aid, not a substitute for the exact log. When two symptoms overlap, follow the earliest explicit error and test one variable at a time.
What to Send the Server Administrator
When the local checks pass and the data connection still fails, the server operator controls information that you cannot change from FileZilla. Send a concise incident packet:
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- The server hostname and connection type selected in FileZilla, without your password.
- Whether the operation was an upload, download, or directory listing.
- The remote directory and filename, plus the local path where relevant.
- The complete FileZilla log from connection through failure.
- Whether passive mode, the Network Configuration Wizard, and a small test file changed the result.
- Whether the same account works from another approved network.
Ask the administrator to verify the account’s read/write policy, quota, directory ownership, server-side locks, TLS compatibility, and passive-mode address and port range. The administrator can also confirm whether a server firewall permits the negotiated data ports. Providing these details avoids a circular exchange in which each side only sees “connection successful” and “transfer failed.”
After the Transfer Works: Prevent a Repeat
- Keep a known-good passive-mode configuration for networks behind NAT, and document any server-specific exception that requires active mode.
- Use a remote directory whose purpose and permissions are documented rather than relying on a protected system path.
- Preserve the complete log for unusual failures, especially when a provider needs to inspect server-side settings.
- Use FTP over TLS whenever supported, and avoid plain FTP for credentials or sensitive files unless the server operator has confirmed a necessary compatibility exception.
- For scheduled or very large transfers, verify that the computer will not sleep and that network security devices permit sessions of the required duration.
- Test a small file after changing one setting before restarting a large queue. This reduces wasted time and makes the cause visible.
The reliable fix is the one that matches the first specific error: repair the local path for a local read/write failure, correct the remote account or directory policy for a permission failure, and repair the FTP data path for a listing or connection failure after login. The generic queue phrase becomes useful only after that preceding evidence has been identified.
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