How to fix Error 6202 on Windows Server 2025 / Windows 11

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SQL Server 2025 Error 6202: CLR Method Return Value Mismatch

Target Application: Microsoft SQL Server 2025
Operating System: Windows Server 2025 / Windows 11
Error Code: 6202
Message: Method "%ls" of type "%ls" in assembly "%.*ls" does not return a value.

Why This Error Happens

SQL Server raises Error 6202 when a CLR method registered as a scalar function, table-valued function, or user-defined aggregate does not return a value at runtime even though its SQL Server registration (CREATE FUNCTION / CREATE AGGREGATE) declares a return type. This happens when the managed method’s code path falls through without hitting a return statement, when the method is actually declared void but mapped to a non-void SQL type, or when an exception handler swallows the return path. This is strictly a code-level contract mismatch between the .NET assembly and its SQL Server object definition — it is not caused by permissions, ports, or file corruption.

Step-by-Step Resolution Guide

Step 1: Identify the Failing Method

Use the method name, type, and assembly name printed in the error text to locate the exact source file in your Visual Studio / .NET SDK project.

  • Assembly name: taken directly from the third %.*ls token in the error message (e.g., MyClrLibrary)
  • Type name: taken from the second %ls token (e.g., MyClrLibrary.Functions)
  • Method name: taken from the first %ls token (e.g., ComputeChecksum)
  • Open the corresponding .cs or .vb file in your source tree and locate the method with that exact name and type

Step 2: Confirm the SQL Server Registration

Compare the return type declared in the SQL Server object definition against the actual .NET method signature.

  • Check the object definition:
  SELECT OBJECT_DEFINITION(OBJECT_ID('dbo.ComputeChecksum'));
  • Check which assembly and module the function maps to:
  SELECT a.name AS assembly_name,
         am.assembly_class,
         am.assembly_method,
         o.type_desc
  FROM sys.assembly_modules AS am
  JOIN sys.assemblies AS a ON a.assembly_id = am.assembly_id
  JOIN sys.objects AS o ON o.object_id = am.object_id
  WHERE a.name = N'MyClrLibrary';
  • Confirm the SQL return type matches the CLR return type (e.g., SqlInt32, SqlString, or a mapped native type) and is not mistakenly left as void

Step 3: Correct the .NET Method

Ensure every code path in the method returns a value of the type SQL Server expects. Common root causes to check:

  • The method signature is declared void or static void but is registered as a scalar function or aggregate Terminate/Merge method
  • An if/else or switch branch has a path that falls through without a return statement
  • A try/catch block catches an exception and logs it but does not return a value afterward
  • An early return; (with no value) exists inside a method that must return SqlInt32, SqlString, etc.
  • For IBinarySerialize aggregates, verify Terminate() always returns the correct SQL type, not null by default

Step 4: Rebuild and Redeploy the Assembly

Compile the corrected project and update the assembly already registered inside SQL Server.

  • Build the project from a Visual Studio Developer Command Prompt or via the .NET SDK:
  msbuild MyClrLibrary.csproj /p:Configuration=Release
  • Locate the rebuilt binary, typically:
  C:\Projects\MyClrLibrary\bin\Release\MyClrLibrary.dll
  • Update the assembly already registered in the target database using ALTER ASSEMBLY (preferred over dropping and recreating, since it preserves dependent objects):
  ALTER ASSEMBLY MyClrLibrary
  FROM 'C:\Projects\MyClrLibrary\bin\Release\MyClrLibrary.dll'
  WITH PERMISSION_SET = SAFE;
  • If the assembly does not yet support ALTER ASSEMBLY in your environment, drop and recreate it instead:
  DROP FUNCTION dbo.ComputeChecksum;
  DROP ASSEMBLY MyClrLibrary;
  CREATE ASSEMBLY MyClrLibrary
  FROM 'C:\Projects\MyClrLibrary\bin\Release\MyClrLibrary.dll'
  WITH PERMISSION_SET = SAFE;
  CREATE FUNCTION dbo.ComputeChecksum(@input NVARCHAR(4000))
  RETURNS INT
  AS EXTERNAL NAME MyClrLibrary.[MyClrLibrary.Functions].ComputeChecksum;

Step 5: Restart or Reload Affected Components if Needed

CLR assemblies are normally reloaded automatically on the next invocation after ALTER ASSEMBLY, but if sessions still reference the old AppDomain, recycle the SQL Server CLR host or the service.

  • To force the CLR AppDomain for the database to unload without a full service restart:
  ALTER DATABASE YourDatabase SET OFFLINE WITH ROLLBACK IMMEDIATE;
  ALTER DATABASE YourDatabase SET ONLINE;
  • If a full service restart is required, use PowerShell on Windows Server 2025 / Windows 11:
  Restart-Service -Name 'MSSQLSERVER' -Force
  • For a named instance, substitute the correct service name:
  Restart-Service -Name 'MSSQL$INSTANCENAME' -Force

Alternative or Verification Steps

  • Verify the fix: Re-run the statement, query, or stored procedure that originally raised Error 6202 and confirm it completes without the error. Check the SQL Server error log for any new 6202 entries at the default log path:
  C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG

For a named instance, replace MSSQLSERVER with the instance name, or retrieve the active path directly with:

  EXEC xp_readerrorlog 0, 1, N'6202';
  • Alternative if the error persists: Confirm the deployed assembly actually matches the rebuilt binary by comparing the stored hash against the file on disk:
  SELECT name, HASHBYTES('SHA2_256', content) AS content_hash
  FROM sys.assembly_files
  WHERE assembly_id = (SELECT assembly_id FROM sys.assemblies WHERE name = N'MyClrLibrary');

Also check for duplicate or stale assembly registrations in other databases on the same instance, since each database maintains its own independent copy of the assembly and must be updated separately.