i've had the same problem with mine. the shop i bought it from seems to think it could have something to do with it being bypassed. the weird thing is it worked fine up until about two months ago. it started doing it every once in a while, but is happening more often now.
i think it might have something to do with the gps. i noticed once, before i turned the truck off, that it didn't know what time it was, then when i started it back up i got the insert appropriate disk error.