"Cannot access read-only document" message ???

I have an Excel 2000 document that suddenly today won't open. I get a "Cannot access read-only document abc.xls" message when trying to open it. I then get a "cannot access abc.xls" message. I use this file almost daily (yesterday was the last day) and have never saved this file as "read-only". If I try to open it as read-only, I still get the "Cannot access read-only document abc.xls" message, but I don't get the second message.

Other XLS files I saved yesterday load fine. Any ideas on a fix?

Thanks.

Buddy