Don't ignore what Bob Shaw brought up. I've heard of that situation quite a few times. I don't know how to test if there's a DCS signal going to the rails or not, but as he said, you can either: 1) try a different DCS-controlled engine to see if it is recognized and runs under the control of DCS, or 2) change the wires on the TIU for that track to a different set of posts.
= walt