How to fix Error 6232 on Windows Server 2025 / Windows 11

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Why This Error Happens

Error 6232 occurs when a CLR (Common Language Runtime) user-defined type (UDT) is marked for native serialization but is being used in a context that native serialization doesn’t support, such as exceeding the 8,000-byte size limit or being referenced in operations requiring custom marshaling logic. This typically happens after assembly deployment when the Format.Native attribute was applied to a struct containing fields or properties that are incompatible with SQL Server’s native binary layout rules. It can also surface after an in-place upgrade to SQL Server 2025, where stricter CLR type validation exposes previously tolerated schema inconsistencies.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Assembly and Type

  • Run the following query to locate the CLR type causing the conflict:
  SELECT a.name AS AssemblyName, t.name AS TypeName, t.is_binary_ordered
  FROM sys.assembly_types t
  JOIN sys.assemblies a ON t.assembly_id = a.assembly_id;
  • Cross-reference the type name from the error message (%.*ls.%.*ls) with this result set.
  • Check the assembly’s source .cs or .vb file for the [Serializable] and [SqlUserDefinedType(Format.Native)] attributes.

Step 2: Change Serialization Format to Custom

  • Open the Visual Studio project (or source file) for the CLR UDT/UDAGG.
  • Modify the attribute from Format.Native to Format.UserDefined:
  [Serializable]
  [SqlUserDefinedType(Format.UserDefined, MaxByteSize = 8000)]
  public struct MyCustomType : INullable, IBinarySerialize
  • Implement the IBinarySerialize interface (Read and Write methods) to manually control the byte layout, since native serialization no longer applies.
  • Rebuild the assembly (.dll) using the matching .NET runtime version supported by SQL Server 2025 (currently .NET 8 CLR hosting).

Step 3: Redeploy the Assembly in SQL Server

  • Drop the existing type and assembly on the instance:
  DROP TYPE dbo.MyCustomType;
  DROP ASSEMBLY MyAssembly;
  • Re-register the updated assembly with PERMISSION_SET = SAFE (or EXTERNAL_ACCESS if required):
  CREATE ASSEMBLY MyAssembly
  FROM 'C:\SQLAssemblies\MyAssembly.dll'
  WITH PERMISSION_SET = SAFE;
  • Recreate the UDT and any dependent tables/columns referencing it.

Step 4: Validate CLR Strict Security Settings

  • Confirm clr strict security is enabled (default in SQL Server 2025) via sp_configure:
  EXEC sp_configure 'clr strict security';
  • If the assembly is unsigned, sign it with a certificate and create a corresponding login with UNSAFE ASSEMBLY permission, since native serialization failures can sometimes cascade from blocked trust validation.

Alternative or Verification Steps

  • Verify the fix: Re-run the original INSERT/SELECT/CLR operation that triggered Error 6232; confirm no error is raised and check sys.assembly_types to ensure is_binary_ordered = 0 (indicating custom serialization is now active).
  • Alternative workaround: If modifying source code isn’t immediately possible, reduce the UDT’s field footprint (remove large arrays/strings) so it stays within native serialization’s fixed-layout constraints, then redeploy without changing the Format attribute.