GPS not found warning

My system (5 Original heads, HW4 CPU, GPS, Speaker, NetRadar DSPx2) has been running fine for months (years actually). Suddenly, when I started the system today, I am getting a GPS not connected warning. I recycled the system several times and still get the warning. I went to the GPS add-on module and unplugged everything and plugged it back in. I replugged the GPS module (Ver.3) to the HW4 CPU controller and also tried plugging the GPS directly in to the G position on the CPU with the same results. The red light on the GPS antenna (under the hood) is illuminated (constant red, indicating a fault) and all connections seem fine but I'm still getting the warning. I also checked the configurator, and GPS IS selected as on in all three configurations. Has the GPS add-on module or the GPS antenna gone bad? If so, how do I know which to replace?