first thing that springs to mind:
is the show rendered?
you'll get the same "render" issues if it isn't.
next, are you exportng usng QT conversion?
same thing goes for that, as FCP will be attempting to re-calculate all your FX
but maybe ths is just a simple export as QT movie, same settings from a rendered timeline.
sometimes i get a "Gerenal Error" when i try to export.
i just hit OK, and the sign oes away, and the export proceeds.
sometimes i have to hit OK a few times.
in general i suspect this is a RAM / memeory issue,
and is generally brought on by my having too many complex projects / timelines open.
if i close a few projects and timelines other than the one i want to export, i stop getting the warnings.
a whole 1.5 hr movie might be a bit much depending on the complexity.
you could try splitting it up into smaller sections.
nick