ECU Message Mystry

I have a 915is in a new Montaer MC-01 LSA.  I don't have a dongle, but have dual Garmin G3X Touch's on the panel.  I have been getting intermitent CAS (Crew Alert System) messages that say "ECU ALT" and Flashing on Lane B.  At first I thought that it was a bad altimiter setting, but that is not an issue. I contacted Garmin and they said that it is from the ECU and engine ECU specific.  After I reset Lane B it goes away, but then will randomly pop up again. All the engine readings are well within the green arcs.

Any idea of what the ECU is trying to tell me? Is there a list of ECU error codes available anywhere or do I have to find an IRMT with a dongle to call ROTAX? I can download a portion of the Garmin .xls log if that would help.