The quick answer is - the OnStar report occurs once a month and it does not like ANYTHING (Progressive SnapShot, Range Module, DashHawk, DashBoss, etc.) plugged into the OBD2 port when it runs.
The longer answer - OnStar runs diagnostics on the CAN bus at the same "address" as a diagnostic tool plugged into the OBD2 port (makes sense, right?) If something else is plugged into the port, it's like the address slot is already filled, so it can't run it's diagnostics. (Same thing happens with the dealer Tech II and any other device).
This doesn't hurt anything, but it will complain that it can't run diagnostics ... it usually occurs the same time every month and if you want, you can just unplug the module when your report is due that night and then plug it back in the next morning.
The good news is the fact the Range Module can just be unplugged and replugged to cure. It doesn't leave any "footprint" in the ECU and it doesn't modify ANYTHING in any of the modules.