Trouble connecting to PC

[Felix]

I managed to get my new Robobuilder built correctly first time! I have been trying to get it connected to my PC today but I have been having a strange problem. It seems that all of the included programs crash if I try to connect to the Robobuilder when it is using mains power. I have got it in PC control mode (PF1 is blue, PF2 is orange) and have tried using the latest MotionBuilder from the internet. It seems to connect fine when using battery power. For the record I am using an USB to Serial converter to do this.

Any ideas?

EDIT: Hmmm I did manage to get it working with it running on battery power but I can't seem to repeat this either. The programs take longer than usual to come up with the box saying "COM3 Try to connect...", and then get stuck there. If it does manage to connect then the robot goes into some crouching position (PF1 and PF2 go off and the run light somes on) when it seems to become unresponsive and I get a Serial check failure

[Felix]

Despite the manual telling me to put it in PC control mode before connecting it to a PC, it seems to work if I just leave it in HUNO mode and let MotionBuilder change the mode for me. OneArmHandstand is go!