How to fix Error 6590 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 6590 – DROP ASSEMBLY Failed Due to Object Reference

Why This Error Happens

This error occurs because SQL Server enforces strict dependency tracking for CLR integration objects, and the assembly you are attempting to drop is still bound to one or more database objects such as stored procedures, functions, triggers, or user-defined types. SQL Server 2025 will not allow a DROP ASSEMBLY operation to complete if doing so would orphan these dependent objects, as it would break their underlying implementation. This typically happens when a developer forgets to remove or alter dependent CLR objects before attempting to clean up or redeploy an assembly.

Step-by-Step Resolution Guide

Step 1: Identify the Dependent Objects

  • Run the following query to find exactly what is referencing the assembly:
  • SELECT o.name, o.type_desc FROM sys.sql_modules m INNER JOIN sys.objects o ON m.object_id = o.object_id WHERE m.assembly_class IS NOT NULL;
  • Alternatively, query sys.assembly_modules joined with sys.assemblies to map the assembly name directly to the dependent procedure or function names referenced in the error message.

Step 2: Drop or Alter the Dependent Objects

  • For stored procedures or functions, execute DROP PROCEDURE [dbo].[YourProcedureName]; or DROP FUNCTION [dbo].[YourFunctionName]; for each object identified in Step 1.
  • If the object is a CLR-based User-Defined Type (UDT) or Aggregate, you may need to drop any tables or columns using that type first before the type itself can be removed.
  • Ensure you are connected to the correct database context (USE YourDatabaseName;) before running these commands, as dependencies are scoped per-database.

Step 3: Retry the DROP ASSEMBLY Command

  • Once all dependent objects are removed, execute the original command again: DROP ASSEMBLY [YourAssemblyName];
  • If the assembly still fails to drop, check for dependencies in other databases on the same instance, as a single assembly file can sometimes be referenced across multiple contexts if improperly scoped.

Step 4: Use CASCADE Option for Bulk Cleanup (Optional)

  • If you intend to remove the assembly along with all its dependencies in one transaction, use the cascading drop syntax instead of manually deleting each object: DROP ASSEMBLY [YourAssemblyName] WITH CASCADE;
  • Note: Use this with caution in production environments, as it will automatically drop all functions, procedures, and triggers associated with that assembly without further confirmation prompts.

Alternative or Verification Steps

  • Verification: After the DROP ASSEMBLY command succeeds, run SELECT * FROM sys.assemblies WHERE name = 'YourAssemblyName'; to confirm the assembly no longer appears in the result set.
  • Alternative: If you cannot identify the dependency via T-SQL, open SQL Server Management Studio (SSMS), navigate to Object Explorer > Databases > [YourDB] > Programmability > Assemblies, right-click the assembly, and select View Dependencies to visually inspect and resolve the blocking objects.