This thread really helped me. When my project refused to open and hung up FCP6, what worked for me was:
1. moving the project file to the desktop,
2. disconnecting the media harddrive,
3. I had to go into FCP preferences, change the scratch disk to a different hard drive.
4. Then open the project from the desktop.
5. Then I re-connected the media.
For some reason all that worked fine.