Is there a known problem with the units overheating? I bought a 2011 disc from Naviupdates and I've only used it twice. I used it this weekend and after about 1/2 hour the message on the screen came up saying disc unreadable. I tried it on the computer and it read it fine. I tried it in the car a couple of hours later and it worked to start with, then the message came up again but this time the unit locked, as though it had crashed. Today, it was running continuously on a 5 hour journey with no problems. It was a warm day when it crashed and it's a lot cooler today, that's the only difference I can come up with.