Well, depending on what is driving pin-2 on J4, having that connected to an output could have cooked it. Connecting pin-2 on the CC-M to another output port is a major no-no.
At this point, I'd try the second CC-M, but WITHOUT connecting pin 2 to anything. With the IR tether disconnected from anything, see if the CC-M sees the serial data. You can leave the tender totally out of the mix for now, we just want to get the locomotive working. Usually, it's the IR tether that loads the serial output enough that the CC-M doesn't see the serial signal. Once you get that far, we can then go ahead and connect the IR tether to pin-2 and see if the tender see serial data.
It's not out of the realm of possibility that you simply got a bad CC-M, occasionally I get a bad board from Lionel, MTH, and yes, ERR.
These kinds of issues are why I still get lots of work. 
