VSS Error 12293 hr = 0x80070020

Good Morning,

I've got an Hyper-V 2012 R2 Cluster, which I am backing up with Veeam Backup & Replication. All ist working fine, but on Server 2008 with Terminal Server role installed.

I'm trying to create a vss consistent backup, but the Microsoft CSV Shadow Copy Provider turns out an error and in the Event log of the terminal Server is the following error:

VSS Error 12293 hr = 0x80070020

I installed all patches and Hotfixes. I even changed the disk signature and so on. I'm running out of Options...any ideas what could might help?

Thanks for your help,

lenny