iPhone Accessory warning - without any accessory I am getting following error:



Previously I connected iPhone headphone/handsfree. It was working fine. Now, I disconnected my headphone/handsfree &amp; my iPhone started giving warning as follows. 

I am not sure what's wrong with the phone. I have restarted iPhone many many times, but anything didn't work. I am not able to talk with iPhone without handsfree. iPhone forcing me to use handsfree.
I think the problem is caused by circuit shortening on the iPhone dock connector. This means that the iPhone detects some kind of an accessory is connected (pin shortened), but cannot verify that it's genuine. Try cleaning it with compressed air.