Windows 11 KB5077181 SENS Login Error System Event Notification Service

What is the KB5077181 SENS Login Error?

After installing the Windows 11 February 2026 cumulative update KB5077181 (builds 26200.7840 and 26100.7840), some users encounter a login failure caused by the System Event Notification Service (SENS). The error message states that a specified procedure could not be found, blocking the sign-in process entirely.

SENS is a Windows component that monitors system events for COM+ applications and delivers notifications for logon, logoff, network, and power events. When KB5077181 corrupts a dependency in the SENS service chain, the login sequence breaks even though the operating system boots normally — meaning you may have already resolved the KB5077181 boot loop only to hit this second wall.

When does it occur?

• Immediately after signing in — the desktop briefly appears then drops back to the lock screen
• After the KB5077181 boot loop has been resolved but before a clean login succeeds
• On devices running Windows 11 24H2 (build 26100) or 25H2 (build 26200) with the February 2026 patch
• On machines where SENS dependencies were already in a fragile state before the update
• After automatic restart following the KB5077181 installation

Common causes

• KB5077181 overwrites or corrupts a DLL that SENS depends on (typically sensapi.dll or sens.dll)
• The SENS service dependency chain breaks when the Servicing Stack Update (SSU) applies out of order
• A corrupted Component Based Servicing (CBS) store prevents clean service registration
• Third-party security software interferes with the update's service reconfiguration
• Previous failed update attempts leave orphaned registry entries under HKLM\SYSTEM\CurrentControlSet\Services\SENS
• System File Checker (SFC) has not been run after prior cumulative update failures

Step-by-step fixes

1. Uninstall KB5077181 from Windows Recovery Environment (WinRE) — Restart your PC and hold Shift while clicking Restart (or force three failed boots to trigger WinRE). Navigate to Troubleshoot > Advanced Options > Uninstall Updates > Uninstall latest quality update. Alternatively, open Command Prompt from WinRE and run: wusa /uninstall /kb:5077181 /quiet /norestart

1. Manually restart the SENS service — If you can reach Safe Mode (F8 during boot or via WinRE > Startup Settings), open an elevated Command Prompt and run: net stop SENS && net start SENS. Check the result with sc query SENS — the state should show RUNNING.

1. Repair SENS registry entries — In Safe Mode, open Registry Editor and navigate to HKLM\SYSTEM\CurrentControlSet\Services\SENS. Verify that the ImagePath value is %SystemRoot%\system32\svchost.exe -k netsvcs and that Start is set to 2 (Automatic). If the DependOnService multi-string value is missing, add EventSystem as a dependency.

1. Re-register SENS DLLs — In an elevated Command Prompt, run: regsvr32 /s %SystemRoot%\system32\sens.dll then regsvr32 /s %SystemRoot%\system32\sensapi.dll. Restart the computer.

1. Run SFC and DISM repair sequence — Open an elevated Command Prompt and run in order: DISM /Online /Cleanup-Image /RestoreHealth (wait for completion), then sfc /scannow. This repairs corrupted system files that KB5077181 may have damaged.

1. Reset Windows Update components — Stop the update services: net stop wuauserv && net stop cryptSvc && net stop bits && net stop msiserver. Rename the cache folders: ren %SystemRoot%\SoftwareDistribution SoftwareDistribution.old and ren %SystemRoot%\System32\catroot2 catroot2.old. Restart the services and retry the update.

1. Pause Windows Update — After uninstalling KB5077181, go to Settings > Windows Update > Pause updates and pause for at least 2 weeks to prevent automatic reinstallation while Microsoft releases a corrected build.

1. Check for a replacement update — Visit the Microsoft Update Catalog at catalog.update.microsoft.com and search for a superseding update for KB5077181. Microsoft typically releases an out-of-band fix within 1-2 weeks of widespread reports.

If it still doesn't work

If the SENS error persists after all the steps above, perform an in-place repair install by mounting the Windows 11 ISO matching your build version and running setup.exe with the Keep personal files and apps option. This reinstalls Windows system files without affecting your data. You can also try creating a new local administrator account from Safe Mode Command Prompt using net user TempAdmin Password123! /add and net localgroup Administrators TempAdmin /add, then logging in with that account to verify whether the issue is profile-specific. For enterprise environments, contact Microsoft Support and reference KB5077181 SENS regression — Microsoft is actively tracking this issue.