Thank you for those screenshots !
It looks like your configuration and addressing are all correct, but the ladder logic that manages the MSG instructions is causing your problems.
Your MicroLogix 1400 screenshot shows that the .EW bit is set for that MSG instruction control block. The "Enabled and Waiting" status bit indicates that this particular MSG instruction is waiting for an available communications buffer in the controller operating system.
I know the SLC-5/03,4,5 controllers had just 4 simultaneous message buffers. I'm not sure how many the MicroLogix 1400 has.
I can't see the ladder logic you are using, but the fact that you are using an OTU (unlatch output) instruction addressed to the Enable bit suggests that you are re-triggering the MSG continuously.
While this method is often shown in sample logic (including in some Rockwell reference manuals) it is not appropriate for systems that need to communicate with large numbers of remote devices. Your program list shows several routine names that suggest that your MicroLogix is communicating with an ABB device and the PLC-5/40 and maybe with other devices.
Examine the MicroLogix 1400 program and see how many MSG instructions you have, and change them to logic that does not automatically re-trigger them by unlatching the Enable bit. In my opinion, the only MSG instruction status bit that should ever be manipulated in logic is the .TO bit, which causes the message to go through an orderly shutdown as though it has timed out at the operating system level.