How to fix Error 6592 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 6592

Why This Error Happens

Error 6592 occurs when SQL Server’s CLR integration attempts to access a property or field on a .NET object within an assembly, but the specified member does not exist or is inaccessible at that type’s current version. This is typically caused by a mismatch between the assembly loaded in SQL Server and the actual source code it was compiled from, often resulting from an outdated or incorrectly registered assembly (DLL) following a code change, partial deployment, or serialization issue with CLR user-defined types (UDTs) or user-defined aggregates (UDAs). Corrupted metadata in the sys.assemblies catalog or a failed assembly update can also trigger this error.

Step-by-Step Resolution Guide

Step 1: Verify the Assembly Version Currently Loaded in SQL Server

  • Run the following query to inspect assembly details: SELECT name, create_date, modify_date FROM sys.assemblies WHERE name = 'YourAssemblyName';
  • Compare the modify_date against your local build timestamp of the .dll file to confirm whether SQL Server is using a stale version.
  • Check sys.assembly_files to review the binary content hash if versioning is suspected.

Step 2: Drop and Re-register the Assembly

  • Script out and drop any dependent CLR objects (functions, types, aggregates) referencing the assembly using DROP AGGREGATE, DROP FUNCTION, or DROP TYPE.
  • Remove the outdated assembly: DROP ASSEMBLY YourAssemblyName;
  • Re-add the corrected assembly from the compiled source: CREATE ASSEMBLY YourAssemblyName FROM 'C:\Path\To\YourAssembly.dll' WITH PERMISSION_SET = SAFE;
  • Recreate all dependent CLR objects that were dropped in the previous step.

Step 3: Rebuild the .NET Project with Matching Serialization Attributes

  • Open the source project in Visual Studio and confirm that the [Serializable] and [SqlUserDefinedType] attributes match the fields referenced in the T-SQL definitions.
  • Ensure that public properties/fields referenced by SQL Server (e.g., in Parse() or ToString() methods) have not been renamed, removed, or set to private instead of public.
  • Rebuild the solution in Release mode and redeploy the updated .dll to the SQL Server host directory.

Step 4: Clear the Plan Cache and Restart the SQL Server Service

  • Flush cached execution plans that may reference the old assembly metadata: DBCC FREEPROCCACHE;
  • Restart the SQL Server (MSSQLSERVER) service via Windows Services (services.msc) on Windows Server 2025 to ensure the CLR host reloads all assemblies cleanly.
  • If running on Windows 11 for a local development instance, restart via PowerShell: Restart-Service -Name 'MSSQLSERVER' -Force.

Alternative or Verification Steps

  • To verify the fix, execute the stored procedure, function, or query that previously triggered Error 6592 and confirm it returns data without exceptions; check the SQL Server Error Log (via xp_readerrorlog) for any residual CLR loading warnings.
  • If the error persists, enable clr strict security validation checks and use ALTER ASSEMBLY ... WITH UNCHECKED DATA as a temporary bypass only in non-production environments while you identify the exact schema mismatch between the deployed binary and the database metadata.