Hmm, perhaps this is not a network error. After all, the connection has been established. You write that only this machine is causing trouble and others from the same source Hyper-V have been converted to the same destination, haven't they? Besides you have attempted to convert that machine several times. If all that is correct, may be there is something specific with this particular machine. As a workaround, you may try to power it on and convert it as physical.
If you would like further investigation, I suggest you send the VM to the tech support guys, we'll get it from them.
HTH
Plamen