Compressor Problem suddenly -- help!

Am new to Mac and FCP, just cut a 40-something minute documentary, am trying to export a Quicktime h.264 version to send to my transcriber, using compressor. I did this before easily at the start of the project, when I compressed 18 hours of interviews to H.264 100 kbps, no problem.

Now that I have an edited show, when I try to encode, I get a FAIL message and an Error 50.

I've searched around here and on the Apple site, came across people talking about a similar problem but have been unable to find any solution that's worked for me.

Any ideas? Why would this suddenly stop working? Or does it have to do with some problem in my timeline?

Many thanks,
Jeff
ps: running latest FCP & compressor on a new Mac Pro w/5 gigs of ram.

PS: The exact error when it fails is "QuickTime Error: -50" I'm running Quicktime 7.1.5 by the way

<<<Quicktime 7.1.5>>>

Is that the QuickTime you started out with?

OSX, FCP, QT Upgrades?

Koz

Thanks, not sure whether I started with this quicktime or not, to be honest.

OXS version 10.4.9
FCP 5.1.4
not sure if I've upgraded quicktime, don't think so. When I check "about quicktime" it says I'm running QuickTime 7 Pro, registered to Apple Pro Apps User with the reg code "automatic."

??

I uninstalled/reinstalled Compressor, still can't do h.264...