Today one of the user reported that he is unable to connect to a VM. When I checked (VM -> edit settings -> I found the Network card was not connected. It was unchecked). I was unable to ‘check’ it. When I tried to check, I got the below error: Invalid configuration for device ‘0’.
VM -> Edit settings -> Remove the NIC card -> ok
VM -> Edit settings -> Add a NIC card -> ok
This resolved the issue.