I located this exact issue in KB article 819853 -
http://support.microsoft.com/default.aspx?kbid=819853

The KB article describes exactly the circumstances here.
However, the KB article states that SP3 will fix the
issue. I was running SP3 when I was bitten. I do not have
the files (excelop.msp and excelff.msp) on my system, but
the version of Excel.exe is 10.0.6501-- later than the
one shown in the KB article.

Excel is apparently able to open the file, albeit with
the pivot table not functioning. So I'm unable to move
the pivot fields around and the drop menus are not
functioning. I can't save the repaired file with another
name, or in another directory, even with the sheet
containing the pivot table deleted; I get "Document not
saved" message.

This would not be a huge issue, save for the fact that
this workbook is a part of a larger suite of reports that
are referenced in an Add-In. Changing the file name would
require altering many lines of the VBA Project code, as
well as deviate from a particular naming convention. I
realize I may have to do just that, but I was wondering
if perhaps someone had encountered this and knows of a
different workaround than "Turn Off Auto-recover." The
information in the KB article didn't help much besides
alluding to a Hotfix I can't seem to find.

Thanks in advance,
Michelle