Several Ubuntu 10.04 VMs were restarted after few months and began getting "Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)" message. Restoring those VMs from backup (to the "paused" state) allows to boot normally. However restarting the VM again results in the mentioned error message. I suspect it's the updated kernel version (2.6.32-37-server, 2.6.32-38-server) that misbehave - another Ubuntu VM (that's used as template for those failing VMs) still has 2.6.32-24-server and reboots fine. We're using HyperV (2008R2) as the server host. Nothing were changed in it's configuration. Has anyone faced this issue, please advise the solution. Many Thanks in advance!