most likely the problem is a corrupted render file. it happens to us a lot with using the desaturation filter, but it could be one of a million things.
steps:
1) render your timeline using the same export settings you want for the final output
2) export using “quicktime movie, current settings” – but only export small sections at a time, 2 minutes or so
3) when you reach a “general error” during the export look thru your timeline at that export section and drill down until you find the corrupted render
4) the fix is usually as simple as turning the clip filter off and then back on again, rerendering, then goto step 2, repeat
-karl