Hello Tom and mimco,
The data sheet for the GR16A device does specify a baud rate of 7200 when an external crystal of 8MHz or 4MHz is used. However, if a 4MHz crystal is actually in use, it might also pay to also check monitor mode communications at 3600 baud just in case PTB4 remains set high.
If the MON08 circuitry has been newly constructed, it is always possible for there to be a wiring error causing the problem. But this is likely to be difficult to sort from the potential communication problems that Peg mentioned. The MON08 circuit really needs to be initially tested in conjunction with a "real" serial port, to separate the two possible issues, and prove the MON08 circuit.
Regards,
Mac