Excel 2007 Attachment Is Corrupt

Hello:
Running Outlook 2007, Excel 2007 and Windows 7 Professional (64-bit). I have an email that has an Excel spreadsheet attachment (in .xls format). When I try to open it I receive the following message:
"The document is corrupt and cannot be opened. To try and repair it, use the Open and Repair command in the Open dialog box and select Extract Data when prompted."
This is only occurring under Windows 7. I can open the spreadsheet without any problem in XP (also running Outlook 2007 and Excel 2007) as well as in Google Docs. However, if I save the attachment and then open it, I get this message:
"Excel found unreadable content in "Spreadsheet.xls". Do you want to recover the contents of this workbook? If you trust the source of this workbook, click Yes."
Clicking "Yes" opens the spreadsheet.
This appears to be happening just with this particular spreadsheet, however this doesn't explain why it opens with no problem in XP.What should I do to investigate the cause of this? Thank you!