This drives me crazy!. For the longest time I've never had the ability to charge my Iphone 3gs because I was using a cheap Ebay cable. No problem I knew that but then I decided one day to do something about it so I bought a genuine Apple Composite AV Cable and when I plugged my phone in Walah Problem solved!. Charging. However now I've noticed that maybe 1 out of 5 times I plug in it will tell me this Accessory does not support charging!. WTF!. If I sit there and unplug and replug it back in about 10 or so times eventually it will trigger the charge and be fine. But this is getting old. Lately I've had to reboot the phone just to get it to start charging when plugged into the Avic.

WTF! Is it the Phone, Cable or Avic?

Its a connection issue either with the cable or the connector on the phone. If you have a case on the phone take it off and see if that changes anything.

WTF! Is it the Phone, Cable or Avic?

well if it is a apple cable, then it is not the AVIC. its either gonna be the phone or the cable.

i second removing the case, a lot of cases can interfere with the dock cable being plugged in by not allowing the connector to seat properly, check that first. if that doesn't fix it, i would exchange the cable next, if that doesn't fix it, then the dock connector might be starting to fail on the phone.