I belive the GO18WA has its transmit and receive pins reversed at the controller.(yes its wired that way :-) )

You need to make up a DMX reversing lead, with the plus and minus connections reversed at one connector only so transmit becomes receive and visa versa.

Also place a terminator (120 ohms officially resistor) in an XLR connector and terminate the last fixture with that.

That should fix the problem.

The instructions with this controller are apalling for a novice.