Help me diagnose map read error on NAV?

Hi guys,

My 2010 Prius, package IV is only 2 1/2 years old, but I'm at 46K miles, so I don't believe my warranty will cover this (PLEASE correct me if I'm wrong).

My factory NAV system has worked fine, but last week when I tried using it, the display said "Map read error", or "Can't read map" (something like that). I ejected the map disc (ver 8.1), cleaned it, reinserted, and got the same error.

My friend also has a '10 Prius, so he let me try his disc. He's got ver 9.1. When I loaded it, the map came up on the display, but the system locked up when I tried to do anything. I had to restart the car, but when I tried again, the same lockup happened with his disc.

Is there anything special I need to do when loading a new DVD map version? Is there any chance it's NOT the actual head unit that's now bad? Is there any chance my dealer would cover this even though I'm over 36K miles, but not over 3 years?

Any suggestions would be appreciated.

Thanks