Word 2003 default extension is .doc
Newer versions of office use the .docx extension.
Did you install this recently?
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint File Formats
Install this compatibility pack if you would like to open, edit, and save documents, workbooks, and presentations that were created in the newer versions of Word, Excel, and PowerPoint. Scroll down to see instructions and system requirements.
Or could your documents have been created in a newer version of word? In which case you would need to install the above software.
Edited by rotor123, 11 July 2012 - 01:02 PM.