O2 Sensor replaced, then ECM replaced, CEL still on

What is your question?

2005 Chrysler Town and Country LX 3.3 liter engine 190k miles Check Engine Light (CEL) was on, failed emissions test in Tennessee, O2 sensor showed as the problem. My mechanic (not the dealership) replaced the O2 sensor. The CEL came on immediately afterward. My mechanic traced the problem to the only thing they could figure which was a bad Engine Control Module/Powertrain Control Module (ECM/PCM) (two different names for the same thing, I think). I ordered a rebuilt ECM from a reputable company on eBay. My mechanic installed it and the CEL again came on immediately afterward. My mechanic is stumped. I wonder if my original ECM was even bad. The dealership charges over $90 just to check the ECM and can only check the one that is on the vehicle; not the one that was replaced. The eBay company has a tech support line, and I left three messages on Friday afternoon. I haven't received a response yet. What else could this be? Thanks in advance!