tuneflex car mount: worked for 2 songs!

[Skipper]

Hey, i just went down to the apple store to see if i could find a mount for my car. Now i know that sometimes products made for ipod work for iphone, so I got the tune flex car mount. It plugs into the cigarette lighter and has the line out port right there for an auxilary input. When I set it all up and docked my phone, everything worked perfectly, it would even play, charge and ring through the stereo when a call came in. But then about 2 songs in it just stopped. It still said it was playing, and when I took it off it would switch back to the speaker on the phone..... But that just boggled me.
does anyone know why? I just figured the line out function worked the same on the iphone, maybe not?

Thanks in advance!