1: Serial port incorrectly configured. Ensure that the serial port is set to the correct port within the script device, and that the corresponding port is set to GUI Two way RS232 on a PC4, and that the baud rate is set to 9600, with 8 data bits, no parity and 1 stop bit (data bits, parity and stop bit only relevant on PC1/PC2s)
2: If serial port configuration has been checked and deemed correct, check wiring. Buzz out the cable again ensuring that you have pin 5 going to ground and pins 2 and 3 for transmit and receive. If this is correct ensure you have pins 2 and 3 wired in the correct manner, i.e. try reversing if you are not receiving communication as expected.
3: Also make sure your using the latest CBUS Module 3.5.7 and above as this sends a command string to set the MODE of the PCI correctly.