Exception: A serious error has occurred? And restarting doesn't work.

I'm right at the end of project and I keep getting this warning: Exception: A serious error has occurred! It is recommended that you immediately save your work and restart the system.

Ok, I've started and re-started 5 times. I've deleted my site settings, MC State, and Site Attributes. It's just when I try and play my main timeline that I get this error. I can grab the timeline indicator and drag it around and see video. When I hit the lock key, I can hear audio when I drag. But when I hit the play button on both the keyboard and the monitor play button, I get that error. I can open individual clips in the preview monitor and play them and I can toggle the timeline and play them. Other sequences play just fine but it's just that one sequence which happens to be my main timeline. I've tried creating another timeline and used the clipboard monitor to paste the offending sequence into a new one but I still get the same error.

I'm working with H.264 files from a Cannon T3i and used Link to AMA. I'm using an iMac 3.4 GHz i7, 16 GB or RAM and using Lion 10.7.3.

Any help would be tremendously appreciated.

quinnmcguee