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Whenever I change the network configuration to NAT for a virtual machine running under Virtual PC 2007, I get "A duplicate name exists on the network." error.

There is no other machine on my network with this name and running the VM in any other network configuration doesn't cause this error.

This seems to be a common problem with Virtual PC 2007 based on a google search but no-one seems to have a solution to it.

So far, I've discovered that turning off NETBIOS over TCP causes the problem to go away but I need to join this VM to a domain and you can't do that if NETBIOS over TCP is turned off.

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I don't think NetBIOS over TCP is required for domain membership, is it? I believe it's only required if you need browsing. – phoebus Dec 18 '09 at 1:29

Windows domains store the list of computers in a complex series of master-browser and secondary-browser lists. The problem is when you change the network config to NAT or vice-versa, the virtual adapter in the virtual image is restarted. However, the lists of computer names translations is not updated yet, so the computer detects its OWN name as duplicate.

Just wait awhile. The computers that cache the name will eventually flush the name and it will be available again.

There might be a way to force the name to flush, but i am not familiar how to do it ..

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This doesn't seem to be the culprit. It's not happening as a result of switching back and forth to NAT and no matter how long I wait, the problem does not resolve. – Phred Menyhert Dec 21 '09 at 19:08

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