There isn't anything wrong with that controller. It's just older and has been replaced by newer hardware.
Because it is older, you will need to use older software. Your Studio 5000 version 31 won't work with it. RSLogix 5000 version 20 was mentioned, but you must use the version that matches the firmware version of your controller. If your controller has firmware version 19.xx, then you require RSLogix version 19.xx. Version 20 wouldn't help you there. The good news is that the firmware can be updated. So, you could update your controller to the newest possible version 20 and then use RSLogix 5000 version 20 software. If you can browse to the device in RSLinx you can verify its version.
The reason we are concerned with using that controller is in part, getting spares would be difficult since it is discontinued. That controller series was not extensively used, so the third-party market for spares probably isn't overflowing with available parts.
But like I said, there isn't anything wrong with those controllers. Most likely it was gathering dust on a shelf, and someone decided to put it to use.
OG