When I plug my USB cable to my car from my droid x I get reading error from my car
I had a business trip tn a rental car this past week which had a USB port on the stereo. I plugged in and tried all 4 options (PC Mode, Windows Media, USB Storage, and Charge Only) and all of them gave the same error message on the car's stereo that you describe. So I was only able to use the stereo's USB port to charge the phone.
Instead, I used the 3.5mm stereo jack to play the phone's music, nav, calls, etc to the car's audio. If your car does not have a 3.5mm connector, you can get one installed in most cars for $100-200. The guy installed mine so that the cables hide in the glove compartment when not in use, and he didn't have to drill any holes.
Yeah I'm trying to find a FM transmitter App to do this. My friend does it with his iphone and said droid should have a app too. to stream bluetooth way.