Through trial and error I have found the answer to the problem.

To start, I use UBEC's to power my receivers. I originally tested the system using my standard UBEC and the GSU did not work. I sent it in and had it back within 7 days with the report there was nothing wrong with the GSU ( I was impressed with the turnoround speed ) . I had been having troubles ( another matter ) with LiFe and NiCad receiver packs making my servos jitter. The UBEC did not have this problem. After getting the unit back and it still not working, I plugged in an old Nicad and the GSU started working. I then changed the jumper on the UBEC to 5.6 v and the unit worked. There seems to be a low voltage threshold at about 5v for the unit to work. I could find nothing in the manuel or online dealing with receiver voltages.
My problem has been solved. I hope noone else encounters this.
John