USB error

[washingtonHERO]

I am trying to hook my phone up to my car stereo which has a USB port. I am just using the USB cord that came with the wall charger, but everytime that I try to plug it in it says USB error on my stereo. Just wondering if anyone else has had these kind of problems or what other options could I use to hook my phone to my car stereo (I do not have an AUX port in my car). thanks for any help!