Thanks for the reply!
To answer your questions: Haven´t burnt in the past, because the blu-ray writer is new. Also the program Express Burn (with registration). Trying to create a new Blu-ray disc with data from my hard disk.
I work on a mac, so I didn´t delete the folders you named above, but I deleted the program and reinstalled it. And restartet 2 times as you described.
But still the same. Error saying that there seems to be no disc in the drive...
Any other recommendations?