I can access this old Allen Bradley SLC 150 with the PCIS software installed in my PC running ME and a standard serial port using a 1745-PCC interface. However, the same software installed on a laptop running XP with a USB to serial converter doesn't work. USB port is on COM1, 9600 baud, parity none, stop bits 1. I can use this USB/ serial port to communicate with newer Micrologix and Koyo PLCs with no problem. With the SLC 150, the PCIS program locks up whenever I attempt to save, clear, monitor or read the SLC program. Any ideas?