The same has happened to me.
FCP 5 shuts down when exporting a HDV timeline using QuickTime Conversion and freezes while exporting the HDV timeline QuickTime movie.
I copied and pasted the HDV timeline to SD and after a 14 HOUR RENDER (what the hell???) was able to successfully use QuickTime Conversion.
Still can’t do any kind of exporting of the HD timeline and the green canvas is getting very irritating.
Stupid QuickTime.
WHY???????