Dash reads ECM data link Prob

So here is the problem. I have a 91 olds 98 elite with only 82,000 miles on it and it does have the digital dash. It is a very nice car and ran fine when I bought it. About 2 months after I bought it I was turned on the car and started to drive and a message came across the dash that said "ECM data link Prob". It was running a little funny so I replaced the ECM thinking that was probably the problem the car then ran great but the ECM Data link Prob message never went away. I have tried unplugging the battery of course to reset the computer but that did not work. I had a mechanic look at it but he could not find anything wrong, I have checked the digital dash but it looks fine, check the wires as much as possible but there are probably a couple hundred that run to the ECM I have also looked at the Data link connector. I do not physically see anything wrong with the wire and the car runs great.
Here is the thing When the ECM light is not on the digital dash works but as soon as the ECM message comes on the digital dash does not work. I have also noticed that when it is warm outside the light does not come on but as soon as night hits and the temp drops the ECM message comes up (I live in Ohio so right now it is about 65ish)
I am really just wondering if any one has had this problem or knows where I should look next. I just am a little lost. Thanks in advance