Troubleshooting Guide: SQL Server Error 6554 – “SQL Assembly Name” Error

Why This Error Happens

Error 6554 occurs when SQL Server’s CLR (Common Language Runtime) integration encounters an assembly that fails validation due to a mismatch in permission sets, such as attempting to load an UNSAFE or EXTERNAL_ACCESS assembly without the proper trust configuration. This is commonly triggered by the TRUSTWORTHY database setting being disabled or the assembly lacking a valid strong-name signature with a corresponding asymmetric key or certificate mapped to a login with UNSAFE ASSEMBLY permission. Corrupted or incompatible assembly binaries compiled against a different .NET runtime version than what SQL Server 2025 supports can also trigger this failure.

Step-by-Step Resolution Guide

Step 1: Verify Database Trustworthy and CLR Settings

• Open SQL Server Management Studio (SSMS) and connect to your Windows Server 2025 instance.
• Run the following to check CLR status:

  sp_configure 'clr enabled';

• If disabled, enable it:

  sp_configure 'clr enabled', 1;
  RECONFIGURE;

• Check if the database is marked trustworthy:

  SELECT name, is_trustworthy_on FROM sys.databases WHERE name = 'YourDatabaseName';

Step 2: Fix Assembly Permission Set Mismatch

• Avoid setting TRUSTWORTHY ON in production; instead, use a signed assembly with a certificate.
• Create an asymmetric key from the assembly DLL on disk:

  CREATE ASYMMETRIC KEY MyAsmKey
  FROM EXECUTABLE FILE = 'C:\Assemblies\YourAssembly.dll';

• Create a login from this key and grant the required permission:

  CREATE LOGIN MyAsmLogin FROM ASYMMETRIC KEY MyAsmKey;
  GRANT UNSAFE ASSEMBLY TO MyAsmLogin;

Step 3: Re-register or Re-deploy the Faulty Assembly

• Drop the problematic assembly if it already exists:

  DROP ASSEMBLY YourAssemblyName;

• Re-create the assembly explicitly specifying the correct permission set:

  CREATE ASSEMBLY YourAssemblyName
  FROM 'C:\Assemblies\YourAssembly.dll'
  WITH PERMISSION_SET = EXTERNAL_ACCESS;

• Ensure the DLL file is not blocked by Windows (right-click the file in File Explorer → Properties → check “Unblock” if present).

Step 4: Validate .NET Runtime Compatibility

• Confirm the assembly was compiled against a CLR version supported by SQL Server 2025 (.NET Framework 4.8 or the compatible CLR runtime bundled with SQL Server 2025).
• Use corflags.exe (from Visual Studio Developer Command Prompt) to inspect the DLL’s target runtime version if unsure.
• Recompile the assembly targeting the correct framework version if a mismatch is found.

Alternative or Verification Steps

• After redeployment, run SELECT * FROM sys.assemblies WHERE name = 'YourAssemblyName'; to confirm the assembly loads without error and shows the correct permission_set_desc.
• If the issue persists, as a temporary diagnostic workaround (not recommended long-term), set ALTER DATABASE YourDatabaseName SET TRUSTWORTHY ON; to isolate whether the issue is permission-based versus a corrupted binary.