The software in the Alpine/Acura Navi is far from bug-free. At least the Acura version has a "watchdog" which detects a stuck program and reboots the system. My old Alpine CD-ROM version would sometimes just hang and do nothing until you turn your car all the way off and start it up again.
If it happens more than once or twice a month, see if you can exactly replicate the problem. It's difficult to determine exactly how an error occurs, because so many things are happening at the same time -- map redraws, route calculations, reading off the media, GPS tracking, etc. But I remember that Alpine's software was very sensitive to input timing (i.e. they had a thread-safety problem). Make your inputs slowly and avoid inputs during the inital map redraw.
Once you've determined how you can replicate the problem, call the Acura navi dept. and leave a bug report. Unfortunately there's not much you can do about it. Unless Alpine can replicate your problem, the chances are slim that they'll ever find an obscure bug.
Also, see if you can get a free DVD upgrade from your dealer. Sometimes changing the data read from the DVD is enough to knock the bug "somewhere else" where you won't see it again. It's not a fix, but you won't have to deal with the problem.
Remember, there's no such thing as bug-free software!