Hi Mala,

re:
> Where is the mistake?

Hard to tell without being able to examine the model.

But probably an n-gon face somewhere instead of all quads.

I'd recommend to do the sub-d modeling in Cinema4D instead, where you can find documentation and tutorials to help you. Then if you need to do some work combining it with other elements inside MoI use SubD > Create > From file in Moi to bring the subd surface into MoI.

- Michael