Ah, the file is corrupted. Or is it? maybe, maybe not. Here are a few solutions that you can use to help remedy this issue. These could occur in just about any program in the Office suite. It should be noted that this error can occur for numerous reasons and not all of them mean that the file is even corrupted (misleading error messages).
Office 2010 Only
You can have the Office product try to repair the file if it is indeed corrupt.