Have the same issue. Server is running on version 3.1-43/1d4b0dfb (running kernel: 2.6.32-27-pve). Installed vm's: 2012r2 as DC, two vm's with pfsenese as routers, ubuntu 12.04 as fileserver, 2008r2 clean install. All vm's have latest update. Windows and ubuntu vm's running on VIRTIO NICs and HDD, all HDD in RAW mode w/o cache. Problem with communication failure status happening only on w2008 machine, but system working fine - I can connect with RDP, VNC. After I recieved communication failure message and click status on another vm - status displayed normally on all other vm's, then I click back on 2008 and error message returns.