Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
What is the exact error message you are getting?
Are you using FCP? What version?
Also what version of OS X?
Ok, and the file is stored on the hard drive too, or on an external drive?
Can you open any other projects ok?
Check all cables carefully on the Mac and restart it.
If the problem persists, try resetting the SMC & PRAM:1. Shut down the computer.2. Unplug the computer's power cord.3. Wait fifteen seconds.4. Attach the computer's power cord.5. Wait five seconds, then press the power button to turn on the computer.6. Press and hold the Command-Option-P-R keys before the gray screen appears.7. Hold the keys down until the computer restarts.8. Release the keys.
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Ok, then please try resetting the SMC & PRAM.
Yes that's it - .fcpbundle
Can you still open any other projects ok?
Do you have a backup copy of the affected project?