chain slippage

Hi,

I've got a 'Carrera Kraken' mountain bike and i keep getting this problem
where the chain seems to 'slip' around the chain set when in certain gear
combinations.

As I say when in 1 or 3 on the front gears it doesnt do it, but put it in 2
on the front and apply any pressure to the pedals and the chain seems to
slip right round the teeth on the gear wheel and so not provide any drive to
the wheels.

Someone has said that this is due to worn gear teeth, but i dont fully buy
that because they dont seem worn to me, and its been doing it a while and
was doing it occasionally when the bike was new.

Any idea why this happens?


Thanks
Jeremy