Saving issue w/ Excel 2003

One of our users is having an issue within Excel 2003. He tried to save one of his documents, but when he tried to pull up the document at a later time, an old version of the document appeared instead of the one that he had saved. The only thing I could think of would be that maybe during an upgrade from Excel 2000 to 2003, maybe something did not transfer correctly. Any ideas why a saved file would revert back to an older file and not show the most recently saved document? I was told that the new document appears for a split second, but then disappears and the old version of the file appears instead.