I have read the sticky thread regarding this subject, but it seems to have lost some steam. I would like to add my comments. I too have had this problem. I bought my vette November 10, 2011, from Carmax. Within 2 weeks, I started getting the signals. Finally after taking it to a few place, I was able to get the specific codes:

U2100, U21005, U2107, and U2108. All comm codes. One dealership I took it to gave me these codes and some specific instructions they received from GM techs to fix my problem. Keep in mind, this after I had the recall problem taken care of. That has not fixed my problem either. Anyway, here is what the Tech II wrote down and give me a copy:

U2100, U21005, U2107, and U2108
Ck Elect inputs to ECM-BCM-EBCM
Input Connector C180
Ck for any open & shut electrical
Drag test Terminal ECM-BCM-EBCM
Ck 2500 & 2501
Something BCM-EBCM EBCM-ECOM
Ck complete wiring harness
ck modules before disconnect

I have no idea what all that means, but they wanted to charge me 300 dallors, after I had already paid them a 100 dallor dedecutable for a privious visit for the same problem, but they did not know what codes were being affected. They simply stated the fixe was charging the battery, com check, no problem. So, when I got the message again, I took it immediately to the dealership, the idenified the codes listed and later I took it back to them. It is this time they called the GM tech's, got the troubleshooting instructions I mentioned, and wanted to charge me. Nope, I told them to stop, I will pick it up, and did, took it back to Carmax, and they supposely fixed the problem given the fact I gave them a copy of the codes and checklist. We shall see. I have had the car back now going on 3 days, so far, so good.

I thought I would share these codes and ck list to see if it can help you all who is having the same problem.