I'm currently editing Danny Wilcox Frazier's multimedia version of Driftless. The project includes lots of beautiful video, shot by a professional DP in 24p anamorphic format with a DV codec. We've blown the the 4:3 standard footage up to 16:9 1080 high-definition, while retaining the 24 frames-per-second frame rate. The footage is now being edited with Apple's ProRes 422 codec for faster renders and to compensate for the unusual frame size. We've also desaturated the video so that it matches Danny's gorgeous black-and-white photography. Needless to say, there's a lot going on with the Final Cut timeline.
So it wasn't a total surprise when my Final Cut suddenly suddenly refused to play through an entire sequence. The playhead continued to stop at the exact timecode and a pop-up window informed me that I had a "general error." I searched the internets for an explanation, trashed preferences, replaced clips, all to no avail. The timeline continued to stop in the same location each time.
Finally, I exported the timeline as XML, then reimported. After that, the timeline worked just fine, playing all the way through without issue.
I'm not exactly sure what the lesson is here other than whatever your problem might be, don't hesitate to try everything.