Error when relocating virtual machine on VI ESX 3.5

I was facing the need to move machines from one SAN LUN to another, but kept on hitting an error where the vCenter server just keeps saying “Cannot connect to host” after trying to use the “migrate” option, both with the guest machine being turned on and off. It seems to be some kind of time-out it’s waiting for – after approx. 5-10 minutes. The first ESX is running 3.5.0 64607 and the other one is a lot newer running 3.5.0 207095. The vCenter 4 is running update 1.

Luckily we have another ESX 3.5 server on the same location, so I tried to add it to the inventory under the other host. After this it was possible to move the machine and then remove it from the inventory again, and add it to the original host and started it up.

I have not been able to find an explanation in any log-files, configuration files or on the VmWare community or anywhere on the internet, but as far as I can see there can be two: Either this version of ESX doesn’t support Storage-vmotion, both “hot or cold”, or the other option is that somewhere in the configuration, I am missing a setting – the server was moved from one site to another, with another IP-segment, but I haven’t found a lot more things that doesn’t work and I would expect this if there was some major configuration error.