Recently I upgraded to Office 2010. In Excel I receive a corrupt error when opening files, in particular if the files are emailed and attached to the email and then download.
The best fix and the only one that appears t work is to do this:
1. Right-click on the file in windows explorer and go to Properties for the file;
2. On the first tab (“General”) at the bottom there was text that stated “This file came from another computer and might be blocked to help protect this computer”, next to the text was an “Unblock” button. Selecting “Unblock” solved this issue.

Try it and see how it works.