How to fix Error 4141 on Windows Server 2025 / Windows 11

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Why This Error Happens

Error 4141 occurs when a CLR user-defined type (UDT) or CLR trigger attempts to modify its own data or schema while already executing within the context of another CLR operation on the same type. SQL Server’s CLR integration layer explicitly blocks recursive or nested ALTER/UPDATE operations against CLR types to prevent state corruption and deadlocks within the SQLCLR hosting environment. This is typically triggered by poorly designed trigger logic, recursive stored procedure calls, or an assembly that attempts self-referential updates during an active transaction.

Step-by-Step Resolution Guide

Step 1: Identify the Offending CLR Object

  • Open SQL Server Management Studio (SSMS) and run the following query to locate active CLR assemblies and types:
  SELECT * FROM sys.assemblies;
  SELECT * FROM sys.assembly_types;
  • Review the SQL Server Error Log (C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG) for the exact transaction or stored procedure name tied to Error 4141.
  • Cross-reference the stack trace with any custom CLR triggers (sys.triggers where type_desc = 'CLR_TRIGGER').

Step 2: Review and Refactor the CLR Trigger/Procedure Logic

  • Open the source code project (usually a .cs or .vb SQLCLR project) in Visual Studio 2022/2025.
  • Check for any method that calls SqlContext.Pipe.ExecuteAndSend() or performs an UPDATE/ALTER on the same CLR type from within another CLR method already modifying that type.
  • Remove or restructure recursive calls — move the secondary update logic into a separate transaction scope outside the original CLR context using SqlConnection with Context Connection=false.

Step 3: Rebuild and Redeploy the Assembly

  • In Visual Studio, right-click the SQLCLR project and select Rebuild.
  • Deploy the updated .dll using:
  ALTER ASSEMBLY YourAssemblyName
  FROM 'C:\Deploy\YourAssembly.dll'
  WITH PERMISSION_SET = SAFE;
  • Restart the SQL Server service via Services.msc (SQL Server (MSSQLSERVER)) to clear any cached CLR execution contexts.

Step 4: Adjust CLR Strict Security Settings (If Applicable)

  • Open a new query window in SSMS and verify CLR strict security configuration:
  EXEC sp_configure 'clr strict security', 0;
  RECONFIGURE;
  • Note: Only disable strict security temporarily for testing on Windows Server 2025; re-enable it after confirming the fix (sp_configure 'clr strict security', 1;) for production security compliance.

Alternative or Verification Steps

  • Re-run the original transaction or trigger that caused Error 4141 and confirm it completes without nested update exceptions in the Activity Monitor.
  • If the error persists, drop and recreate the CLR type entirely using DROP TYPE followed by CREATE TYPE ... EXTERNAL NAME, ensuring no overlapping transaction scopes exist in the assembly’s Invoke methods.