KB Article: http://support.microsoft.com/kb/2387587
When you try to open an Excel, Word, or PowerPoint 2010 file from Outlook or from the Internet, Office reports the file as being corrupted and cannot be opened. Although the error message is different for each application, the result is the same. Errors may include the following:
"The file is corrupted and cannot be opened."
"Word Experienced an error trying to open the file."
"PowerPoint found a problem with content in <filename>. PowerPoint can attempt to repair the presentation."