How to fix Error 2581 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 2581 – “DBCC cannot free the DLL”

Why This Error Happens

This error occurs when you attempt to run DBCC FREESYSTEMCACHE or DBCC FREEPROCCACHE targeting an Extended Stored Procedure (XP) DLL that SQL Server believes is no longer loaded into memory. This typically happens because the DLL was already unloaded automatically by SQL Server due to inactivity, or because the reference in sys.dm_os_loaded_modules is stale and does not match the actual process memory space. In some cases, this is triggered by a mismatch between the DLL name casing/path provided in the command and the internal module registry.

Step-by-Step Resolution Guide

Step 1: Verify the DLL Status in Memory

  • Query the system view to confirm if the DLL is actually loaded before attempting to free it.
  • Run the following T-SQL command: SELECT * FROM sys.dm_os_loaded_modules WHERE name LIKE '%YourDLLName%';
  • If the result set is empty, the DLL has already been unloaded, and the command is unnecessary.

Step 2: Check for Case Sensitivity and Path Errors

  • Ensure the DLL name used in the DBCC FREESYSTEMCACHE command exactly matches the case and extension found in the sys.dm_os_loaded_modules view.
  • Navigate to the Binn directory to verify the physical file exists: C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Binn\
  • Re-run the command using the exact string copied directly from the DMV query results.

Step 3: Restart the SQL Server Service to Clear Stale References

  • If the registry reference remains stale despite the DLL being unloaded, a soft restart of the service will clear the internal cache.
  • Open Services.msc on Windows Server 2025.
  • Locate SQL Server (MSSQLSERVER), right-click, and select Restart.
  • Alternatively, use PowerShell: Restart-Service -Name 'MSSQLSERVER' -Force

Step 4: Check Windows Event Viewer for Access Denied Flags

  • Open the Windows Event Viewer and navigate to Windows Logs > Application.
  • Filter for Event ID 2581 to see if it is paired with an Access Denied error, which suggests Windows 11/Server 2025 security policies are blocking the handle release.
  • If found, verify that the SQL Server service account has “Full Control” permissions on the specific DLL file via the Security tab in File Properties.

Alternative or Verification Steps

  • Verification: Re-run SELECT * FROM sys.dm_os_loaded_modules; after the restart to confirm the specific DLL entry is completely absent from the list, verifying the cache is clean.
  • Alternative: If the error persists only in specific user sessions, bypass the command entirely by using DBCC FREEPROCCACHE without specific parameters to clear the global plan cache instead of targeting the specific module.