Hi Marius!
I have seen this behavior when using the scheduler.
The account used while backing up has to have 'full control' access on the
drive's root.
So, if you want to backup the c: drive manually, the account you use should
have full control on C:\ (Don't select include subdirectories!)
If you use the ADSM Scheduler you should give the SYSTEM account full
control access for all roots on all the drives.
Kindest regards,
Eric van Loon