Can't backup Db

[wislndixie]

For some unexplained reason, Access won't let me backup my db. It's worked fine for months, but now when I try to backup my db I get the following message: "could not use <filename>, file already in use". I'm the only user and I've closed the db, waited and then reopened and try to backup again and still can't. Hope someone can help me solve this.
thanks,
Wisln

[rpeare]

before you do anything else, make a copy of that database.

Once that's done, try a compact and repair on one of the copies then run through your backup procedure again