Yes, when I started it manually all works fine.
I also re-scheduled it and let it run while I was watching, and (ofcourse...) it also ran fine again.
The tapes I'm using aren't new ones.
As a test I've tried to manually erase one of the tapes that 'didn't work', and guess what....once again no problem.
So I'm a bit confused now.....all things seems to be ok, they all work fine when done manually, but for some reason it just didn't work 2 times in a row.