Originally Posted by
Ajax
ACE is the database engine - previously Access used JET.
Only other thing I can suggest it to try and open the db in exclusive mode. Open access, browse to your file and in the bottom right, select the exclusive option.
Otherwise, sounds like your db is corrupted, can you revert to a backup? if not I think you have a problem. Once you do get up and running again, I strongly recommend you split the db, keep a spare copy of the frontend somewhere and regularly backup the backend - it reduces the chances of corruption and improves the opportunity to recover, even for single users.