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 resource which contains different guides, solutions... click here Project Repair Toolbox