Hey All,
Something that just snagged me, and gave me the exact same error was FCP’s time remapping. We just upgraded to the new FCP, I opened a job from a couple months ago that need changing. All of my timelines but one would export, the odd man out kept giving me a general error.
I took the steps above, rendering clip by clip to find the culprit, and sure enough it was on a clip that had its speed changed. I brought a fresh instance of the clip down, and tried to put the same speed settings on (I think the previous editor to this piece was using 20463%). FCP gave me an error, saying it capped out at 10000%. I set the new clip to this max, and all was well.
I’m guessing that the previous FCP let you go hog wild with your speed changes and the new one’s a bit more careful with the new speed controls.