Hi Patrick:
Could be some particular aspect or combination of aspects about the file, ...
its size
any macros
functions
udf's
Data Tables,
Pivot tables
Calc Status
..........
can you think of any thing that's peculiar about this file that might be causing this behavior?
If it is a single worksheet you might try moving it to a new workbook and saving that workbook.
If there are several worksheets, you still might try, moving the worksheets to a new workbook, save and reopen.
Before you do all this, how about if you quit Excel, rrestart and open the same workbook;
and if that does not work, how about quit Excel, shut the copmputer down, restart, open Excel and then open the workbook
Well, Good Luck!