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Troubleshooting

"Execution of user code in the .NET Framework is disabled"​

CLR isn't enabled on the instance:

EXEC sp_configure 'clr enabled', 1;
RECONFIGURE;

CREATE ASSEMBLY fails with a strict-security error​

CREATE or ALTER ASSEMBLY for assembly ... failed because assembly ... is not authorized for PERMISSION_SET = SAFE.

This is CLR strict security on SQL Server 2017+. Sign the assembly and grant UNSAFE ASSEMBLY to the key's login, or (dev only) register the hash with sp_add_trusted_assembly. Full walkthrough in Security.

"Assembly ... was not found in the SQL catalog"​

Your assembly references another DLL that isn't registered. Dependencies must be CREATE ASSEMBLY'd first (supported .NET Framework libraries are already available; everything else must be registered explicitly). Keep dependency graphs shallow — ideally none.

NullReferenceException from a function​

Almost always a raw CLR type used where NULL can arrive. Take SqlString, SqlInt32, etc., and check IsNull before .Value — see Core Concepts.

First call after idle is slow​

The app domain was unloaded (memory pressure or idle timeout) and is being re-created and JIT-compiled. Confirm in sys.dm_clr_appdomains; it's normal. If it happens constantly, the server is under memory pressure — investigate with sys.dm_os_memory_clerks.

"Data access is not allowed in this context"​

The function performed data access without declaring it:

[SqlFunction(DataAccess = DataAccessKind.Read)]

Or it attempted data access somewhere it's not allowed (e.g. inside certain function contexts). Declare honestly and re-deploy.

Still stuck?​

  • Check sys.dm_clr_loaded_assemblies, sys.dm_clr_appdomains, and the SQL Server error log — CLR unload/reload events are recorded there.
  • The FAQ covers conceptual questions.
  • The general troubleshooting guide covers site-wide issues.