I'll second that - 6.3.0.2 is pretty good - well, lets say it's up with an average 5.5 release - a few more tries and they might make it to the best of the 5.5's - actaully, to be fair, the current release seems to have no obvious vices.
I'm sure that looking over the past progress, I remember saying "I'd rather have 6.0.0.15 with the overburn patch, than 6.0.0.19" - with 6.0.0.23 and up to current, all progress seems to have been in the right direction.
So I'll echo the advice - do NOT bother trying to debug Nero 6 version below 6.3.0.2 - just upgrade and see if that resolves it ... a big download, but worth the wait.