I believe that your issue has been addressed before. Vista outputs ArtNet lighting data over the top most network interface in the list in System Preferences, so if that top network interface is WiFi, the ArtNet data will be sent over WiFi and your lights will not be controllable. The simple fix is to go to Network in System Preferences and reorder the list of network interfaces so that Ethernet is at the top. This way, even when WiFi is on, the lighting data will still be sent over Ethernet.
See this post by Ben Coleman for more info:
Hope that helps!
Drew