This is an issue that keeps re-occuring.....

Catalyst will connect to the newtork at the top of the 'service order' as specified in network preferences. There is no way to specify one network connection for Artnet, and another connection for SYNC

refer to thread:
http://chaldee1.gotadsl.co.uk/~richa...&highlight=sam

what other networking features are you using?
do you have remote desktop enabled?

Simon