Sorry to steal the thread, but this has just happened to me on the way home.
I've just started using an unofficial iPod wire (the kind you get with an airport connector on a pullstring) with my head unit, seeing as my other one fell to pieces.
Its been fine, more practical if anything, but the odd time, it just turns the whole headunit off, and a few dash lights come up.
It did it tonight, i didn't have my iPod in and then all the interior lights went off on the car. Then it went into limp mode as i was pulling out of a junction, so i had to turn off the ignition and re-start the car.
But now the annoying light is on with the squiggly line, but the car still starts fine. (i hope)
How do i turn it off?