Hyper-V Cluster 2012R2 / Bent 2014: The Virtual Machine resource is not responding. Backup set canceled.

Hi!

I have a Windows Server 2012 R2 Hyper-V Cluster. Backup is done by using Bent 2014. Unfortunately, I get the following error:
V-79-57344-65304 - The Virtual Machine resource is not responding. Backup set canceled.

Inside the VM I see the following error in the event viewer:
The disk signature of disk 1 is equal to the disk signature of disk 0 (Event ID 58 partmgr)

Backup is then aborted for this VM.

Any help is is highly appreciated!!

martin