Microsoft Safety Scanner and Windows Defender scans may stop unexpectedly with error code 0x8050800c, halting virus checks and leaving systems unprotected. This error often signals a conflict in system state, outdated definitions, or interference from third-party antivirus tools. Addressing the underlying causes restores proper scan functionality and improves system security.

Update Windows and Microsoft Defender Definitions

Step 1: Open the Windows Settings panel by pressing Windows + I. Navigate to Windows Update and click Check for updates to allow Windows to install any pending updates. Keeping your system and security definitions current resolves compatibility and scan issues introduced by outdated files.

Step 2: After updates install, restart your computer to ensure all changes take effect. Restarting also resets system state, which can clear transient errors that block scans.

Remove Conflicting Third-Party Antivirus Software

Conflicts between Windows Defender and other antivirus tools are a primary cause of error 0x8050800c. Microsoft Defender will not run scans if another real-time antivirus is registered on the system, even if the other antivirus is disabled.

Step 1: Open Settings and go to Apps before selecting Installed Apps on the right. Review the installed programs list for any third-party antivirus products (such as Norton, McAfee, AVG, or trial versions pre-installed by your PC manufacturer).

Step 2: Select each antivirus program and choose Uninstall. Follow the prompts to remove the software. For some products, it's necessary to use the vendor’s dedicated removal tool to eliminate all components. Refer to the vendor’s website or Microsoft’s list of antivirus cleanup utilities for links to these tools.

Step 3: Restart your computer after uninstalling each antivirus program, even if not prompted. This step ensures all services and drivers are fully removed from memory.

Step 4: Open Windows Security and confirm that Microsoft Defender is now the active virus protection provider. If Defender is not active, select Turn on and check for updates again.

Run System File Checker and DISM to Repair Corruption

Corrupted system files or Windows components can prevent Microsoft Defender and Safety Scanner from running scans. Running built-in repair tools identifies and fixes these issues.

Step 1: Type CMD in the Start menu, right-click Command Prompt, and select Run as administrator.

Step 2: In the elevated Command Prompt, enter the following command to check for and repair system file corruption:

sfc /scannow

This scan may take several minutes. Allow it to finish and follow any prompts if repairs are made.

Step 3: After the SFC scan, run the Deployment Imaging Service and Management Tool (DISM) to fix deeper Windows image issues. Enter the following command:

dism.exe /Online /Cleanup-image /Restorehealth

Wait for DISM to complete. If errors are repaired, restart your PC before trying another scan with Microsoft Defender or Safety Scanner.

Restart the Computer and Retry the Scan

According to Microsoft’s official troubleshooting, error 0x8050800c can result from a system state that blocks scans in your current user context. Restarting the computer resets the environment and may resolve the problem.

Step 1: Save any open work and restart your computer using the Start > Power > Restart menu.

Step 2: After rebooting, launch Microsoft Defender or the Microsoft Safety Scanner and attempt the scan again. If the error persists, proceed with the next methods.

Perform a Clean Boot to Eliminate Startup Conflicts

Background applications or services can interfere with Defender scans, especially if remnants of security software remain. A clean boot starts Windows with only essential services and drivers, isolating the cause.

Step 1: Press Windows + R to open the Run dialog, type msconfig, and press OK.

Step 2: In the System Configuration window, switch to the Services tab. Check the box labeled Hide all Microsoft services to avoid disabling critical system services.

Step 3: Click Disable all to turn off all remaining non-Microsoft services. Click Apply to save changes.

Step 4: Go to the Startup tab and click Open Task Manager. In Task Manager, disable each enabled startup item by selecting it and clicking Disable.

Step 5: Close Task Manager and the System Configuration window, then restart your PC. Attempt the scan again. If the scan completes successfully, re-enable services and startup items one at a time to identify the conflicting application.

Download and Use the Latest Version of Microsoft Safety Scanner (MSERT)

Occasionally, error 0x8050800c is caused by a faulty or outdated build of the Microsoft Safety Scanner. Microsoft periodically updates MSERT to address such issues.

Step 1: Visit the official Microsoft Safety Scanner download page at Microsoft Safety Scanner Download.

Step 2: Download the latest version for your system architecture (32-bit or 64-bit). Avoid using previously downloaded copies, as they may be expired or incompatible with your current Defender engine.

Step 3: Run the new MSERT executable and choose your preferred scan type. If you still encounter the error, check the %systemroot%\debug\msert.log file for detailed error codes and cross-reference with Microsoft’s support documentation for targeted troubleshooting.

Additional Tips and Maintenance

  • Verify your system date, time, and time zone settings. Significant discrepancies can prevent security tools from updating or running scans.
  • After resolving the error, schedule regular updates and scans to reduce the risk of future scan failures or malware infections.
  • If you continue to experience issues, consider running Windows Update Troubleshooter or contacting Microsoft Support for advanced diagnostics.

Resolving error 0x8050800c in Windows 11 restores the ability to run security scans and improves your system’s protection. Keeping your system updated and free of conflicting antivirus software helps prevent similar issues in the future.