I have a C182T -2008 model and have had 2 AHRS failures in flight...one in IMC !(Good practice though on standby's)! At first I thought there were spurious heading problems and then eventually the big red X appeared. This IS a known problem with Garmin 1000 ...
AVwebFlash Complete Issue
Have a look at that link and if you need anything else let me know.
Easlily rectified by an approved centre by changing the AHRS unit which takes longer to do the paperwork than the change itself. Make sure you have the G1000 system CD as they will need to re-install the software to the correct configuration from your aircraft.