Trouble with AVIC-N1

I have  the Pioneer AVIC-N1 It has been working fine. Then all of a sudden it keeps telling me to please load the appropriate disk. So i eject the nav disk that came with it that i have been using and it says checking disk. then comes back with please load the right disk. Well at times it works fine and then maybe after i shut truck off and turn it back on it will go all stupid like that again. Then sometimes when it is telling me to load the correct disk i eject it and it will start working again. I was wondering if any of you have ever had this problem and what a fix might be for it.

oh if it really matters it is in a 2003 ford f150

it sounds like the laser eye that reads the discs might be going bad.  I hope not, but if that's the case, I think Pioneer charges an exhorberant $200 to repair if it's out of warranty. 

Has it been really hot where you are at? Check your disc, the heat my have warped it causing these problems.