I really hate posting this old canard, but none of the solutions I have persued have worked yet. Here's my story.
The FE/BE database I am upgrading has locked up on me and won't let me save any changes. Just previous to this happening I had linked a Word document to the front end. Then the messages started appearing. "You do not have exclusive access to the database at this time", yada, yada, yada. No worries yet. I went about closing all related files, Word, Access, Front End, Back End and then reopened the Front End, but still got the same messages. I've tried everything I could think of, Compact and Repair, check for laccb files, Opening Exclusively, rebooting, nothing worked. This database resides on my C: drive. Nobody else is using it right now except me. I'm about ready to suck everything out of it right now into a new accdb file. Actually, I just tried that and THAT didn't work either. Not a happy camper right now.