I've experienced this problem in the last few days with several different VMs. We are running ESX Server 3.5.0, 123630 and VC 2.5.0, 104215.
When I am working through the console with a VM, it will suddenly reboot. The console goes blank and I see nothing until I shut down the console and reopen it. When I do, the machine is in the process of coming back up.
I have a suspicion that this has something to do with the VM being connected to an ISO image on the "Client Device" at the time of the reboot. When the console goes black the message about the CD being disconnected appears. I tried moving the ISO image to a "Datastore ISO file" and did not have the problem.
Has anyone else experienced this issue or know for sure what it is about?
Can you isolate this to a given host ? Does it only happen when connected to the console ?