RQM: Permantly Delete/Purge Test artifacts

Hello,

I try to purge a Test script permanently and get the following message

Deleting Artifacts
Operation Failed
'Delete Work Item' Failed.  Permission Denied.
You don't have permission to perform the following actions:
  any

I did the following:
1) Manage This Project Area - Permissions: check that I have for "Save Test Scripts" all rights, especially "Permanently Delete" right!
2) Open "View Trash"; Select view "Test Script" - select test script and click "Delete Artifact"
3)  confirm message "The selected artifact will be permanently deleted. continue?" - click Delete

Now the error message occurs.
What else is required to permanently delete a test artifact?
We use RQM 4.0.5. thanks!