we're using version 6.0.9. i, as admin, was SO frustrated w/ not being able to delete incorrectly imported pdf files!!
basically, you DO NOT want to left-mouse click on file when it will open up Adobe viewer for you to see document. you want to ONLY right-mouse click on file for options menu to pop up, highlight "delete item" and proceed from there.
i think the bug has something to do w/ Adobe viewer. it generates the error message.