How to fix Error 6253 on Windows Server 2025 / Windows 11

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Microsoft SQL Server 2025 – CLR Initialization Issue (Error 6253)

Why This Error Happens

Error 6253 is logged by SQL Server when the Common Language Runtime (CLR) is initialized for CLR-enabled objects such as SQLCLR assemblies, stored procedures, or user-defined types. While the message itself is informational, it frequently surfaces as a troubleshooting flag when the referenced .NET runtime version does not match what SQL Server 2025 expects, when the CLR host policy is misconfigured, or when a corrupted .NET runtime installation on Windows Server 2025 / Windows 11 causes SQL Server to silently fall back to an unexpected CLR version. In most cases, this stems from outdated .NET Framework or .NET runtime binaries, incorrect clr strict security settings, or permission issues on the runtime installation directory.

Step-by-Step Resolution Guide

Step 1: Verify the CLR Version Being Loaded

  • Open SQL Server Management Studio (SSMS) and run:
  SELECT * FROM sys.dm_os_loaded_modules WHERE name LIKE '%clr%';
  • Cross-check the version shown against the SQL Server 2025 supported CLR version (typically .NET 8+ runtime components bundled with SQL Server).
  • Confirm the path reported in the Event Log (%ls from %ls) points to a valid, non-corrupted installation directory (commonly C:\Windows\Microsoft.NET\Framework64\ or the SQL Server private runtime folder).

Step 2: Enable and Configure CLR Integration Correctly

  • Run the following to ensure CLR integration is properly enabled:
  sp_configure 'show advanced options', 1;
  RECONFIGURE;
  sp_configure 'clr enabled', 1;
  RECONFIGURE;
  sp_configure 'clr strict security', 1;
  RECONFIGURE;
  • Restart the SQL Server (MSSQLSERVER) service via services.msc or:
  Restart-Service -Name 'MSSQLSERVER' -Force

Step 3: Repair or Reinstall the .NET Runtime Dependency

  • Navigate to Control Panel > Programs > Programs and Features on Windows Server 2025 / Windows 11.
  • Locate the installed Microsoft .NET Runtime version tied to SQL Server 2025 and select Repair.
  • If repair fails, uninstall and reinstall the runtime from the official Microsoft .NET download page, ensuring the version matches SQL Server 2025’s minimum requirement (verify via SELECT @@VERSION;).

Step 4: Validate File System Permissions

  • Ensure the SQL Server service account has Read & Execute permissions on:
  C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Binn\
  C:\Windows\Microsoft.NET\
  • Use icacls to confirm and reset permissions if necessary:
  icacls "C:\Windows\Microsoft.NET" /grant "NT SERVICE\MSSQLSERVER:(OI)(CI)RX"

Step 5: Clear and Rebuild CLR Assembly Cache

  • Drop and re-register any custom SQLCLR assemblies that may be referencing a stale runtime path:
  DROP ASSEMBLY IF EXISTS YourAssemblyName;
  CREATE ASSEMBLY YourAssemblyName FROM 'C:\Path\To\YourAssembly.dll' WITH PERMISSION_SET = SAFE;
  • Restart the SQL Server instance to force a clean CLR host re-initialization.

Alternative or Verification Steps

  • Confirm resolution by checking the SQL Server Error Log (EXEC sp_readerrorlog;) for a clean Error 6253 entry showing the correct, expected CLR version and path with no accompanying warnings.
  • If the issue persists, run SELECT * FROM sys.dm_clr_loaded_assemblies; to identify any assembly still pointing to a mismatched or deprecated runtime, and re-deploy it against the current .NET version.