MS Hyper-V: Missing single virtual machine

One single virtual machine is missing on my AMS-Installation. It's neither displayed on AMS console "all vms".

Software: Acronis Backup&Recovery 10 Advanced Server Virtual Edition
AMS is installed on: W2K8R2
Agent is installed on: W2K8R2 with Hyper-V host
VM runs W2K8

The concerned hyper-v server hosts another 2 vms (W2K8, SLES 11) that are displayed without any trouble.

I wonder if somebody has experienced a similar issue, yet.

I would like to suggest the administrator of the concerned vm to check the firewall and if it shares an SID with another vm. Would that be a expedient way to get a resolution?

I'm looking forward for your answers ...