Hmmm - bit odd... A few suggestions:

Do you have it connected directly or through a switch?
Some managed switched can filter broadcast artnet which can cause issues.
Have you done a firmware update on the box thru DMX workshop?
Are you using just one port on the mac to connect? and all others disabled.
Sounds like it could be an issue with the box if you are seeing other devices in catalyst, especially if it's been totally reset.

S