On the Windows menu - click Unhide.

This could be the one reason, you are getting this error message.
Hope this information helps you, let us know!

"cannot open the excel document" wrote:

i cannot open my excel file, its says that i have already opened that
file,but i had never open it yet, why the same things appear in a small
windows in mircosoft excel mian windows. please do give me a solution for
this kind of stuff