One of my customers had an issue with their Hyper-V R2 cluster. Suddenly after starting the backup using DPM 2010, the cluster service on one of the cluster nodes failed. The result was that virtual machines were restarted at the remaining hosts.
I found an article on microsoft.com titled The Cluster service stops unexpectedly on a Windows Server 2008 R2 failover cluster node when you perform multiple backup operations in parallel on a cluster shared volume
The article describes a hotfix which needs to be applied when running either Windows Server 2008 R2 or Windows Server 2008 R2 Service Pack 1 (SP1).
Read the article here.
We applied the hotfix and the problem was fixed!