IPod docking station charges but doesnt play music?

I have the iPod Touch 4G and it works perfectly fine on my old docking station, the iLuv i1898BLK

However, when I try to connect it to my mothers docking station, gear4 PG309BLK, it does not work. It charges it, but does not play the music.
It is the same problem with the docking station I have just bought,the Clarity CSPK19i. Both of the iPod docking stations charge my iPod but do not play music off of them. When you try to play the music, it plays from the iPod as normal.
Is there a problem with my iPod?
Why is it doing this and what can I do to solve it?I