Out of the blue, my excel .xls (97-2003) files are coming up "corrupted" when
I try to open them in Excel 2007, after having saved them successfully. It
started a few days ago. I was working on my Vista Ultimate laptop with a
couple files saved on a networked computer running XP SP2. I had opened the
files successully in the morning and saved my changes. When I tried to open
the files later, Excel said the files could not be opened because they were
corrupted beyond repair.

I pulled the files off the backup disk, saved them to the network computer,
and tried to open them, but with the same error message. I can open the
files off the backup disk with my Vista laptop and save them, but when I try
to open it again with either computer, Excel says they are corrupted.

And then again today, I tried to open another file from the networked
computer, but Excel says it is corrupted, though I hadn't had problems before.

And, more interestingly, I can open other files without a problem, with both
computers. However, as soon as I save it (successfully) and then close the
file, Excel says it is corrupt the next time I try to open the file, from
either computer.

The files are saved in the .xls (97-2003) format.

I have run all the virus scans I can find, with no viruses found. No
spyware either.

I have tried repairing, with no luck either.

I really don't know how else to describe the problem, and can't seem to find
any specific pattern, so I don't even know how to look for a solution.

Oh, and another thing I noticed. It is taking a very long time to open and
save the files, when before they would do so instantly. The files are not
very big either, only around 100 kb.

I would appreciate any and all help.

Thanks!