Hi oziz10,
We did some initial investigation on the problem. There are several links (external references) in the design may be broken. It looks similar to a problem mentioned in this thread:
http://forums.autodesk.com/t5/design-validate-document/if-you-were-offline-during-the-fusion-360-mai...
Could you take a look at the thread and check if it’s the case (“were working offline during May 7 update” & “opened the file on a different computer”)?
If it doesn’t work for you, could you provide a copy of the diagnostic log files after trying to open the file again (so we can see the exact error in the log)? Or if you prefer, you may invite me into the project and we can do more investigation and try to fix the file.

Sorry for the inconvenience and thanks for your patience.
Regards,

Nicolas Xu
Sr. SQA Eng.
Fusion 360 Quality Assurance Team
Autodesk, Inc.