I've had the exact same prob, while using DVD shrink software and DVD cloner to write.........
Haven't quite found software that could beat that, but i have mate that has rival software that works very well...........
i will post more details shortly...........
I recon that is software related!!!
I also noticed that some software is effected by screensavers that are activated. Also look for a setting in the options tab for any thing that allows to switch priory to the DVD prog........