Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsDo not download StartupCheckLibrary.dll from a random DLL site. This startup popup usually means Windows is trying to launch a file through an old startup or scheduled-task entry after the file was removed. The safest documented fix is to use Microsoft Sysinternals Autoruns to remove the stale MicrosoftWindowsApplication ExperienceStartupCheckLibrary entry, restart Windows, and then run a full security scan. The filename has also been used by the Crackonosh coin-mining malware, so restoring a quarantined copy can put an infection back on the computer.
What the StartupCheckLibrary.dll error means
A RunDLL message at sign-in normally identifies a broken launch instruction rather than a Windows component that must be downloaded. Windows still has an instruction to load StartupCheckLibrary.dll, but the target is no longer at the expected location. The instruction may be a scheduled task or another autostart entry that survived an upgrade, cleanup, or antivirus quarantine.
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A Microsoft Q&A case reported the popup after an upgrade to Windows 10 version 1909. The accepted answer identified the scheduled task MicrosoftWindowsApplication ExperienceStartupCheckLibrary as the entry to remove. That explains why deleting the missing file itself, or copying a replacement into a system folder, does not solve the underlying problem: the launch reference remains.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe name alone does not prove that every affected computer is infected. It can be a harmless-looking remnant of a security cleanup, but it deserves a malware check because the same filename has been documented in a malicious persistence chain.
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Should you restore or download the DLL?
No—do not restore it from antivirus quarantine and do not obtain it from an unverified DLL-download site. In the Microsoft Q&A answer dated May 6, 2021, volunteer moderator AW specifically warned that advice to restore the quarantined file was unsafe, describing it as a coin miner. A downloaded DLL may be modified, may not match your Windows build, and can give malware an immediate way to run at logon.
If a security product removed the file, the missing-file popup is consistent with a cleanup artifact: the security product removed the payload but could not remove every startup reference. Removing that reference is safer than recreating the payload. Only a trusted Windows repair mechanism or a verified application installer should ever supply a system file, and neither is the first-line remedy for this particular startup entry.
First-line repair with Microsoft Autoruns
Autoruns is a Microsoft Sysinternals utility that lists programs configured to run at boot or logon, including scheduled tasks and less-visible autostart locations. It gives you a reviewable entry to remove instead of requiring a blind registry edit.
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- Right-click the appropriate Autoruns executable and choose Run as administrator. Administrative rights are needed to inspect and remove some scheduled-task entries.
- Use the filter box and enter
startupcheck. Filtering first reduces the chance of changing an unrelated startup item. - Look for the exact task or autorun reference
MicrosoftWindowsApplication ExperienceStartupCheckLibrary. Confirm that the entry points to the missingStartupCheckLibrary.dllrather than deleting a similarly named, unrelated item. - Delete that stale entry from Autoruns, following the utility’s confirmation prompt. Do not use the registry as a first-line workaround; the accepted Microsoft procedure uses Autoruns and is easier to inspect and reverse.
- Restart Windows and sign in normally. If the popup was caused only by the orphaned reference, it should no longer appear.
Deleting the entry stops that launch attempt; it does not establish whether the missing file was ever malicious. Complete the security checks below even when the message disappears.
What to do after the popup is gone
Run a full security scan
Open Windows Security and start a full scan, or use another reputable security product already installed on the computer. A full scan is especially important when the DLL was quarantined, the computer has used cracked software, or you have noticed other suspicious persistence indicators. Keep detected items quarantined or removed; do not approve a restoration merely to silence the popup.
Review quarantine and recent events
Check your security product’s protection history for the original detection, its location, and the date it was removed. A quarantine event followed by a missing-DLL popup supports the stale-reference explanation, but it is not proof that all related components are gone. If the security product names additional files, tasks, or services, allow it to remove those items and follow its restart instructions.
Update before scanning again
Install current Windows security intelligence and product updates before a second scan. If scans continue to detect related items, disconnect the computer from untrusted networks and use the security product’s remediation or offline-scan option rather than copying files back into place.
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Why malware is part of the diagnosis
The Crackonosh malware report documents a concrete use of this filename. In the described chain, serviceinstaller.exe drops StartupCheckLibrary.DLL; that DLL downloads and runs wksprtcli.dll; and the installer creates the scheduled task MicrosoftWindowsApplication ExperienceStartupCheckLibrary. The task is persistence: it gives the malware a way to launch again when Windows starts or a user logs on.
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The report’s removal checklist includes deleting the StartupCheckLibrary task and startupchecklibrary.dll, together with other Crackonosh files and tasks. Do not treat that list as permission to hunt for and manually delete arbitrary files by name. Malware can place components in different locations, use additional tasks or services, and alter security settings. Let an up-to-date security product identify the complete set, and seek specialist incident-response help if detections return after restart.
The report covers samples compiled from January 31, 2018 through November 23, 2020. Those dates describe the analyzed samples, not the age or prevalence of an infection on your computer today. The filename is therefore a reason for caution, not a diagnosis by itself.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choose the response that matches the evidence
| Situation | Best next action | What it accomplishes | What it does not prove |
|---|---|---|---|
| The popup appeared after an upgrade or cleanup, and scans are clean | Remove the matching Autoruns entry and reboot | Stops Windows from calling a file that is no longer present | It does not prove the deleted file was harmless |
| The DLL was quarantined or the computer used cracked software | Leave it quarantined, remove the stale entry, then run a full scan | Prevents reintroducing the payload and checks for related components | A clean first scan does not establish the original file’s history |
| Repeated detections, unknown tasks or services, or disabled security controls | Use the security product’s complete remediation or offline scan; obtain expert help if detections return | Addresses persistence beyond the one startup reference | Deleting one task alone is not a malware cleanup |
| You are considering a DLL download | Do not download or restore the file; remove the stale launch reference instead | Fixes the popup without executing an untrusted binary | It does not repair unrelated Windows corruption |
Microsoft’s built-in logon troubleshooter
Microsoft also provides a Windows logon recommended troubleshooter for Windows 10 and Windows 11. Microsoft says it addresses logon problems caused by corrupted or missing resource files and repairs those files automatically when the device is detected as eligible. Microsoft also says the troubleshooter cannot be run manually.
That limitation matters here: you cannot force the tool to remove the StartupCheckLibrary scheduled task on demand. If Windows offers the recommended troubleshooting action, allow it to complete, then restart and check the symptom. When the popup specifically names the scheduled task above, Autoruns remains the clearest documented way to remove the stale reference.
If Autoruns finds nothing
Do not create a replacement DLL or start deleting registry values at random. First confirm that Autoruns was run with administrator rights and that the filter is searching for startupcheck, not a longer path with a spelling error. If the message persists, record its complete text and the time it appears, run a full security scan, and inspect protection history for a related detection.
If a scan identifies Crackonosh or another threat, follow the product’s removal workflow for every associated file, task, and service. A missing-file popup can be only one visible remnant of a larger persistence setup. If scans are clean but the error continues, use Microsoft’s supported Windows repair and logon troubleshooting options rather than downloading individual system files.
Common mistakes that make the problem worse
- Restoring the quarantined DLL: this can reactivate the coin-mining payload described in the Microsoft Q&A warning.
- Using a random DLL website: the file may be tampered with, incompatible with your Windows build, or bundled with another threat.
- Deleting only a visible file: the scheduled task or startup instruction can continue producing the same error.
- Deleting registry entries first: an individual commenter suggested a registry workaround, but the accepted Microsoft answer uses Autoruns, which exposes the entry in context.
- Stopping after the popup disappears: symptom-only cleanup does not check for related malware files, tasks, services, or disabled security controls.
What is actually established about this error
The documented Microsoft Q&A question was posted December 16, 2019, and its accepted answer was posted May 6, 2021. It identifies a specific scheduled-task reference and a practical Autoruns fix, but it does not provide an independent success rate or prevalence statistic. No published figure establishes how often current Windows installations show this popup.
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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →The defensible conclusion is narrower and more useful: the popup usually means an autostart reference points to a missing target; a security quarantine can leave that reference behind; and StartupCheckLibrary.dll has also been used in the Crackonosh malware chain. Remove the stale reference with Autoruns, never restore an untrusted copy, and scan whenever the quarantine or other symptoms suggest a possible infection.
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