Gary, the earth from the main board is screwed into the recess of the inverter where the earthing screw is located. That screw is in direct contact with the heat sink which is supposed to be the earthing point. That cable is about 3 meters long. Then the earth travels back to the power point and back up to the house which is about 25 meters away.
I don't know if the power supply is providing a perfect supply, but that might just be part of the problem. Below is a link to the power supply I bought.
http://www.jaycar.com.au/productView.asp?ID=MP3096
The version I have is the 20amp supply.
Today I had a crash of the systems. The ST-I guide camera would not connect, not even the spare and the focusor would not connect either (but that is controlled by the mount hub pro). The main camera though is now connecting, but that has its own USB now. Next step is to go picking off each item until I have it sorted. I'll report back if I find what is going on here. Frustration is nothing compared to what I am feeling at present.