Repeated crashes exporting QT movie

I have a 50 minute 1080i XDCAMEX 1080i60 VBR timeline that is repeatedly crashing my machine when I try to export a QT movie. Of course it generally happens in the last 10% of the export. I've also noticed an increased number of crashes when rendering pieces longer than 15 minutes or so.

Any suggestions? I've tried trashing preferences and repairing disk permissions, trying to avoid reinstall if possible, but at this point seems like only alternative.

thx...jw

Dual Quad core MacPro
10 gigs Ram
Kona 3 bd
Xserve Raid 2.5 TB video drive