General error

FCP 7, OS 10.9.5, QT 10.3...when exporting to QT movie 1920x1080, Prores 442 LT (with chapter markers), after about 10 mins,(90 min. movie) I get a "general error" message with no explanation. I've tried different settings with no difference.
Any idea what the error could be?
Thanks,
Larry

Do you have enough hard drive space on the drive your project is located on (your scratch disc) and also enough space on the drive you're exporting to?

Hard drive space not an issue. I have 2 sequences in same project.
Seq #1 renders & outputs without issue.
Seq #2 renders but will not output to QT movie (with chapter markers).
I have been trying to isolate corrupt clip or transition but so far no luck.
I will output to compressor, then import as a Seq #3, add chapter markers & output to QT,
as a work around.
Thanks,
Larry