By "update" I assume you mean CS4.1. Is that correct?
What are the exact settings (all of them) that you have chosen for your Export?
Though it should not result in what you describe, does the WAB (Work Area Bar) extend the entire Duration of you Sequence?
Try anything but QT. That should solve your problems. Qui(R)cktime is just that, quircky.
Okay, user error - I was trying to write the render out to a drive on my network that somehow lost its sharing.
(Not having any error message was not particularly helpful in any event..)
But why is there no option to Export out to an AVI file (got a QT version, in fact.)
There is, choose Microsoft AVI and DV as codec.
Could this be a Mac?
C'est voila - indeed it is (sorry I didn't mention that). No AVI export on the Mac? How very odd.