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In an OPC Classic connection, Windows error 0x80070005 means “access denied” during COM/DCOM communication. The usual repair is on the OPC client and server: confirm the correct processes and service account, then adjust the OPC server’s DCOM authentication, Launch and Activation permissions, and Access permissions in Component Services. Do not start with Windows System Restore unless the error appeared during that Windows operation; the same code is also used by unrelated servicing and activation failures.
What 0x80070005 means in an OPC connection
OPC Classic uses Microsoft COM/DCOM to let a client communicate with an OPC server, locally or across a network. A client can sometimes launch the OPC server or OpcEnum successfully and still fail with 0x80070005 when it tries to receive a response. That pattern points to an authorization failure after process launch, not necessarily a missing server executable.
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In practice, the block is usually an incorrect DCOM access-control list (ACL), an incompatible authentication level, or an impersonation setting. The ACL may be on the client, the server, or both. A client that can browse part of the server but cannot subscribe to data is not proof that permissions are correct; browsing and data exchange can exercise different identities and DCOM calls.
The code is not specific to OPC. Windows also reports 0x80070005 for System Restore, Windows Update servicing, and activation. Those cases use different control planes and different fixes, so identify the operation before changing permissions.
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Identify the exact topology before changing anything
Write down the following facts. They determine which computer and identity must be repaired.
- Protocol: confirm that this is OPC Classic using COM/DCOM, not an OPC UA connection. OPC UA does not use the same DCOM configuration surface.
- Client computer: the workstation, service host, or gateway running the OPC client.
- Server computer: the computer hosting the OPC server executable. It may be the same machine as the client.
- Server identity: the OPC server program and its DCOM application entry. Record whether browsing uses OpcEnum.
- Client identity: the Windows user or service account that actually runs the client. A scheduled task, Windows service, and interactive desktop session can use different accounts.
- Failure point: note whether the error occurs while enumerating servers, opening a connection, browsing, reading a value, or subscribing to a tag.
Use the Windows Event Viewer and the OPC client’s own log to capture the time of the failure and the server or CLSID involved. This prevents a permission change on the wrong DCOM application from appearing to have fixed the problem.
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Confirm the OPC server process
On the server computer, verify that the OPC server is running and that it is the instance expected by the client. If the client starts the server on demand, watch whether the process starts and then exits. A crashed or stale process can produce an access-denied symptom even when the underlying ACL is correct.
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Check OpcEnum when browsing fails
OpcEnum is commonly involved when a client enumerates available OPC servers. If the error appears during browsing rather than while opening a known server, verify that OpcEnum is present and running on the server where it is expected. A stale OpcEnum or server process can retain an old session. End the stale process, start the service or application again, and retry once before making deeper ACL changes.
Test with a known-good endpoint
Try a server and tag that another client is known to read, or test locally on the server computer if the product supports it. A local success with a remote failure narrows the problem to remote DCOM authentication, network scope, or remote ACLs. A local failure indicates that the server’s own DCOM settings, identity, or local permissions need attention.
Repair OPC DCOM permissions step by step
Make one controlled change at a time and record the original value. You may need administrative rights on both computers.
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- Open Component Services on the server. Press
Win+R, enterdcomcnfg, and press Enter. Open Component Services → Computers → My Computer → DCOM Config. - Locate the correct OPC application. Select the OPC server listed under DCOM Config, open its Properties, and verify that the entry corresponds to the server and CLSID recorded in the client log. Do not change an unrelated OPC entry merely because its display name looks similar.
- Set a compatible authentication level. On the server’s General tab, review Authentication Level. Matrikon’s documented example uses Connect. Use the level required by the OPC vendor and your site’s security policy; do not lower protection broadly just to make a test pass.
- Review Launch and Activation Permissions. Open the Security tab. For Launch and Activation Permissions, choose the custom option and use Edit. Add the actual client account or service identity, then grant only the local and remote launch or activation rights required by the topology. If the client runs as a service, adding your personal interactive account will not help that service.
- Review Access Permissions. In the same Security tab, edit Access Permissions. Add the same required identity and grant the local and remote access rights needed to exchange OPC data. The identity used to launch the server is not always the identity used for subsequent callbacks, so check both sides of the exchange.
- Check the client and server system-wide ACLs. DCOM can apply system-wide Access permissions in addition to the application-specific settings. Review the corresponding Access ACLs on both the client and server computers. The OPC Training Institute also notes that anonymous impersonation settings can lead to 0x80070005; inspect those settings when the application ACLs appear correct but callbacks still fail.
- Use broad entries only as a diagnostic baseline. Legacy vendor examples may list identities such as Everyone, Interactive, Network, and System. Those entries can help prove that the failure is an ACL issue in a controlled maintenance window, but they should not be left as a permanent blanket grant. Prefer the named service account or other identity required by the deployment.
- Restart the complete path. Restart the OPC server and client. If the deployment uses OpcEnum, restart it or restart the related service as well. A process that was already running may retain the old security context until it is restarted.
- Retest in increasing scope. First browse or open the known server, then read a known-good tag, then establish a subscription or reconnect scenario. Record which single permission or authentication change altered the result.
Choose the identity that really needs permission
“The user who is logged on” is not a reliable identity for an OPC service. A Windows service may run as a dedicated domain account, LocalSystem, NetworkService, or another configured account. A gateway launched by a scheduler may use a task-specific account. Check the service’s Log On tab, the scheduled task’s security options, or the client product’s runtime configuration.
For a remote connection, the account must be recognized with the required rights on the server computer. Domain, workgroup, and local-account arrangements can produce different authentication behavior. If the client and server are in separate security contexts, involve the administrator responsible for the domain or local account policy rather than granting anonymous or everyone-wide access as a permanent workaround.
Callbacks deserve special attention. An OPC client may successfully start or contact a server but fail when the server calls back to deliver data. In that case, inspect Access permissions and the callback identity on the client computer as well as Launch and Activation permissions on the server.
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Use the symptom to select the next test
| Observed behavior | Most useful next check | Why |
|---|---|---|
| Server does not appear while browsing | Verify OpcEnum and its DCOM permissions on the server; clear stale OpcEnum processes. | Enumeration may fail before the client reaches the target OPC server. |
| Server appears, but opening it returns 0x80070005 | Check the target server’s Authentication Level and Launch and Activation ACL for the client identity. | The server can be discovered, but activation or the first response is denied. |
| Connection opens, but reads or subscriptions fail | Check Access permissions and callback-related ACLs on both computers. | Data exchange can use a different DCOM call path from initial launch. |
| Local test works; remote test fails | Compare remote launch/access rights, authentication, account scope, and client-side system ACLs. | The server itself is functioning; the remote security boundary is the differentiator. |
| Both local and remote tests fail | Verify the server process, the selected DCOM entry, local ACLs, and the account configured for the client. | A topology-independent failure usually points to the application or local security configuration. |
Tighten the configuration after the test succeeds
Once communication works, remove temporary broad grants and keep the minimum rights required by the OPC design. The OPC Training Institute specifically advises returning temporary permissions to corporate security policy. Record the final account, authentication level, application ACLs, and system-wide changes in the change log so a future hardening policy does not silently remove a required permission.
Do not treat a successful test with Everyone or anonymous access as a finished repair. It demonstrates that authorization was involved, but it leaves the OPC endpoint exposed to more identities than necessary. Replace the diagnostic grant with the dedicated service account or approved group, retest browsing and data delivery, and then close the maintenance window.
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If the message appeared during a Windows operation rather than an OPC client session, use the operation-specific path below. Changing DCOM ACLs will not repair a file, registry, or servicing-permission failure.
| Operation | Scope and identity | Appropriate direction |
|---|---|---|
| OPC Classic communication | Client/server computers; OPC client account, service identity, and DCOM application ACLs | Use dcomcnfg, verify processes, repair authentication, Launch and Activation, and Access permissions. |
| Windows System Restore | Local Windows files and restore components | Investigate the restore log and the specific Windows version. A documented Windows 8.1 case involved a read-only OneDrive desktop.ini; update rollup 2955164 was the documented remedy. This is not an OPC repair. |
| Windows Update | TrustedInstaller, SYSTEM, component-store files, registry entries, services, and policy | Back up first. Microsoft’s documented sequence includes resetting file permissions with icacls, restoring TrustedInstaller ownership, resetting update services and caches, then running DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow. Antivirus locks and policy restrictions can also cause the code. |
| Windows activation | Local DCOM security and the SELF identity | Follow the activation-specific case and restore SELF Local Access and Remote Access in Component Services when that is the identified cause. |
Windows Update and System Restore precautions
If the failure is Windows Update
Do not apply the OPC ACL recipe to Windows Update. Update servicing can be denied access to files, folders, or registry entries when TrustedInstaller or SYSTEM permissions are wrong, component-store permissions are damaged, an antivirus product locks a file, or policy restricts servicing. Back up important data and follow Microsoft’s documented reset sequence for the affected Windows edition. Run the DISM repair before System File Checker as specified in that sequence, and restart when the procedure requires it.
If the failure is System Restore
Check the restore operation’s log, Windows edition, and recent updates. The documented Windows 8.1 example involving a read-only OneDrive desktop.ini was fixed by update rollup 2955164. That narrow cause should not be generalized to every System Restore error, and it does not justify changing an OPC server’s DCOM permissions.
If the failure is activation
Activation can report the same hexadecimal value when the SELF identity lacks required DCOM Local Access or Remote Access. Confirm that activation, rather than OPC, generated the event, then use the activation-specific Component Services repair. Keep this change separate from the OPC application’s ACL so each operation has an auditable security configuration.
Quick Recap
Verification checklist
- The client and server computers are correctly identified, and the connection is confirmed as OPC Classic/DCOM.
- The OPC server process is running; OpcEnum is checked when browsing is involved.
- The DCOM Config entry selected is the actual OPC server used by the client.
- The Authentication Level matches the vendor’s compatibility requirement and site policy.
- The account that really runs the client or service has the needed Launch and Activation rights.
- The same required identity has the needed Access rights, including callback-related rights on the opposite computer.
- The server, client, and OpcEnum processes were restarted after changes.
- Browsing, a known-good read, and a subscription or reconnect were tested separately.
- Temporary broad ACLs were removed and the final least-privilege configuration was documented.
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