I've tried several files, even down to 30 minutes that fail. Others that are longer burn ok. I have a support ticket open, they replied that they have not heard from there engineers as of yet. They did ask if I can burn a DVD via MyDVD Pro (which also fails). Maybe these problems are related?
As soon as I hear back from them I'll update here.
Toast 17 is now 64 bit. Apart from that I see no difference though I haven't used it because of the ongoing problem.