Windows Server 8 allows us to store virtual machines on file shares. As Taylor Brown explains, when you are managing VMs from RSAT on your desktop, and those VMs are running on a host and stored on a file server, then your authentication is between you and the host. The file server doesn’t know who you are and rejects your efforts.
Up to now, un-merged snapshots were the big gotcha in Windows Server 2008/R2 Hyper-V. I suspect this Kerberos “issue” will be the new one, especially because SMB for storing VMs will probably be widely adopted in the breadth market.
The solution is constrained delegation, which is something you’ve been doing if you’ve been sharing ISO files so that VMs can mount them across the network. Taylor Brown goes into some detail on a best practice method for enabling constrained delegation for correctly managing VMs that are stored on an SMB file share.