I have an ESXi 4.1 host with a few servers - two of which are Windows Server 2008 R2 VMs. Server #2 was a copy of Server #1. When I made the clone I'm pretty sure I copied the .vmdk and .vmx files to a new folder via vSphere Client datastore, and then hit 'Add to Inventory' on the .vmx. Each VM starts up and runs Windows, and identifies itself correctly.
However, when I make a change to the settings on Server #2 via vSphere, I receive this error after saving: "File <unspecified filename> was not found". In this case, I was simply changing the network label on the nic. I get the feeling there is some bad juju left-over from the clone, but I'd prefer not to rebuild this server from scratch.