Car USB won't play rooted droid?

My car sterio dock doesn't seem to want to play music off of a rooted droid and I can't seem to figure out why. When I plug my droid (rooted) into my car sterio deck with a USB it says that it isn't supported (it says this on the deck) however if I use an unrooted droid it works, reads, and plays just fine. I've tried using CM6, U.D.7, U.D.8, SS4.8, Shadow Rom 2.1, and Project Elite. It doesn't seem to be a rom issue.

Does anybody know how to fix this or what's not allowing it to play while rooted?

I dont know why it would work with unroot, but not root, but in my car (2009 Lincoln Navigator) I have to use an aux cable to play music with my rooted droid.