BE 2010 R3 Hyper-V GRT Not Working

I have a Hyper-V cluster with about 45 VMs that are all enabled for GRT and are working great. I just built three new VMs in the cluster, and none of them will back up correctly, I get the following:

V-79-57344-38721 - Failed to mount one or more virtual disk images:

Can't seem to find any useful KB articles via search. All the existing VMs are still backing up fine, it's just the new ones that seem to be experiencing this issue.