Mickey's point is important: If it's really a 1747-L531 then it's an SLC-5/03 controller with a DH485 network port, not an SLC-5/05 controller with an Ethernet port.
That's immaterial since you are trying to connect to the Channel 0 RS-232 port.
The error message "not an SLC-500 or MicroLogix controller" generally indicates that the controller firmware ID isn't supported by the version of RSLogix 500 you are using.
I would have preferred that the error message "This SLC-500 is from the Future !", but RSI software developers are terribly literal.
Next questions, then:
What revision of RSLogix 500 are you using ?
What OS Series and Firmware Revision is the controller ?
SLC-5/03 controllers should be at OS Series C, FRN 11 these days.