Excel 2007 Works on Windows Computer But Not On Mac That Runs Parallels

I have a workbook that was created in excel 2007 on a windows 7 computer. Everyday I had been sending the workbook to a mac running windows xp on parallels and the workbook worked perfectly fine. Today when I sent the file from the windows 7 computer to the mac and opened it up from my gmail account the file worked fine. However when I saved the file on the mac and then tried to reopen it I recieved an error that the workbook cannot be opened or repaired by Microsoft Excel because it is currupt. The file still works fine on my windows 7 computer but will not work on the mac. Does anyone have any idea what could be wrong here? I have searched the web for a solution but have found nothing.

So essentially I only get an error when I save and then try to reopen my workbook in parallels. Any ideas?