How to fix Error 6527 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 6527 — “.NET Framework Runtime Has Been Stopped”

Why This Error Happens

This error typically occurs when SQL Server’s CLR (Common Language Runtime) integration encounters a corrupted or mismatched .NET Framework assembly, often triggered by an incomplete Windows Update or a conflicting side-by-side .NET installation. It can also result from insufficient permissions on the SQL Server service account to access CLR-hosted assemblies, or from the clr enabled configuration being improperly toggled during a failed patch cycle. In some cases, a corrupted mscorwks.dll or clr.dll reference within the SQL Server instance causes the runtime host to forcibly halt execution to prevent instance instability.

Step-by-Step Resolution Guide

Step 1: Verify CLR Integration Status

  • Open SQL Server Management Studio (SSMS) and connect to the affected instance.
  • Run the following query to check CLR status:
  sp_configure 'clr enabled';
  • If the run_value is 0, CLR integration is disabled; proceed to re-enable it in Step 2.

Step 2: Re-enable and Reconfigure CLR

  • Execute the following commands in a new query window:
  sp_configure 'show advanced options', 1;
  RECONFIGURE;
  sp_configure 'clr enabled', 1;
  RECONFIGURE;
  • Restart the SQL Server service via SQL Server Configuration Manager (not just the Services app) to ensure the CLR host reinitializes cleanly.

Step 3: Repair the .NET Framework Installation

  • Navigate to Control Panel > Programs > Programs and Features.
  • Select Microsoft .NET Framework 4.8.1 (or the version listed) and choose Repair rather than Uninstall.
  • On Windows Server 2025 / Windows 11, also run:
  DISM /Online /Cleanup-Image /RestoreHealth
  sfc /scannow
  • Reboot the server after the repair completes.

Step 4: Validate SQL Server Service Account Permissions

  • Open services.msc and confirm the account running MSSQLSERVER (or named instance) has local permissions to:
  • C:\Windows\Microsoft.NET\Framework64\v4.0.30319\
  • The SQL Server binaries directory (typically C:\Program Files\Microsoft SQL Server\MSSQL16.MSSQLSERVER\MSSQL\Binn\)
  • Grant Read & Execute permissions if missing, then restart the SQL Server service.

Step 5: Rebuild Corrupted CLR Assemblies (If Applicable)

  • If a custom CLR assembly caused the crash, identify it using:
  SELECT * FROM sys.assemblies WHERE is_user_defined = 1;
  • Drop and re-deploy the assembly:
  DROP ASSEMBLY [YourAssemblyName];
  • Redeploy the assembly from a verified, uncorrupted .dll source file.

Alternative or Verification Steps

  • To verify the fix, check the SQL Server Error Log (via SSMS > Management > SQL Server Logs) for the absence of Error 6527 after a service restart, and confirm CLR functions execute successfully by running a test CLR stored procedure.
  • If the issue persists, consider performing an in-place repair of the SQL Server 2025 instance using the original setup media (Setup.exe /ACTION=REPAIR), which resets core engine files without affecting databases.