Error code -8003

Using a Powerbook with OSX 10.6.8. Trying to delete a long list of back-up files from my external Hard Drive. I pushed "Empty Trash, and get an error message: The operation can’t be completed because an unexpected error occurred (error code -8003).

When I go back to the trash, and try and reverse my action by selecting one of the folders and choosing 'put back', it gives me another message: "The operation can’t be completed because backup items can’t be modified."
So now I can neithermove forward nor move back. How do I get out of this?