Try connecting using PIC/AIC+ driver, it could be port is set to DH485 rather than DF1. I have seen two 5/04 processors with failed RS232 ports, both units approximately manufactured 4-years ago (one straight out of the box, other only been in use a couple of months). I notice the latest version of processor has a spring that connects RS232 circuit to chassis, maybe they had problems with certain earlier versions.