Alternative method (this does not apply for Project 2007 and later versions) only for MS Project 2003...
Save the file in the Microsoft Project Database format:
1. Open your problem file (it may help to turn off automatic calculation if the file is reluctant to open).
2. Select File/Save As...
3. Save as type: Project Database (*.mpd) then click Save.
4. Close the file.
5. Re-open it from the .mpd file.
6. Select File/Save As... And save it as an .mpp file again.
Look at helpful resources which contain different guides, solutions...
http://community.office365.com/en-us/f/172/t/276295.aspx
http://www.filerepairforum.com/forum/microsoft/microsoft-aa/project/1484-ms-project-2010-cannot-open-mpp-file
https://www.repairtoolbox.com/projectrepair.html Project Repair Toolbox