In general, and unfortunately, RSLinx Classic contains a lot of ancient legacy code, and it's a bit of a ungainly thing.
But let's address the DF1 Full Duplex driver, which generally works pretty well.
First, be sure that you have designated the correct COM port; look in the Windows Device Manager to be sure your port is numbered the way you expect.
If it's a USB/RS232 converter, post what exact unit you have. Some work better (especially with Autoconfigure) than others.
The MicroLogix 1000 could be set for Data Highway 485 as well as for DF1 Full or Half Duplex.
When you unplug from its serial port, does the Comms LED go off, or does it flash green ? If it's set for DH485 it will flash about 1/sec when unplugged.
If the MicroLogix came from an application where it was hooked up to a radio or other modem in a multi-drop system, then it might be set up for DF1 Half Duplex Slave, which can be very tricky to connect to even when you have records about the settings.