No clue, it could be anything from firewalls, drivers to network settings. Its outside of the Virtual OS's control so the problem lies with his OS.

Any buggering with his OS's network settings can keep his network connection knocked out and unable to receive 'Techsupport over AIM'. If the server was moved to his normal OS the network issues would be gone- however he won't have a "third party" able to restart or mend the server given the security concerns of "handing over the keys to your Computer".