The rover receiver can't talk to the moving base:
On possible problem is that the port on the moving base that talks to the rover may not be accept 'command' inputs. To
fix this, connect to the moving base using PC-CDU. Go to Configuration->Receiver. Select the 'Ports' tab. Make sure
serial port that is connected to the rover has Input set to 'Command'. Also verify that the baud rate is the same as
what is selected as the moving base baud rate in Carlson Grade. Apply your settings and exit PC-CDU.