It almost sounds like ever since it gave you whatever error message it was that it has stayed in that state. You could always try to do a complete reset of the radio to see if that kicks that error message out. If you completely reset the radio and it still gives you problems then I'd definitely swap it out.
For what it's worth, I was not impressed at all with the Auto EQ results from my AVH-P4200DVD. So, it may be all this trouble to realize the same thing in your case. I'm hoping that they have made improvements in the Auto EQ since the 4200 was released for your sake.
Good luck!