Update - I finally skyped tech support, and they have been great.

The problem appears to be the result of several factors, but is related to switching power supply / 4 motor combo / and a setting on the G540

Gecko are testing out a mod to the G540 to see if they can get it to work with this power supply in particular, and the 4 motors I have.

I'll let you know the result incase others have the same issue.

Nick