The RapidDriver auto-detects all installed parallel ports in operating system. If some port does not appear in the list, that means this port was not properly installed. Anyway, you still have a possibility to add one port to the RapidDriver "by hand" as a custom parallel port.
You must select the port from the list before you perform any parallel port operation. Do not forget to lock selected port to prevent possible clashes between programs wanting to use the same port (you can not lock the "custom" parallel port).