This is a new posting for the same pronblem

I seem to be missing something very very simple, can somebody please look at my attached assembly and explain why I am able to Tangentially mate my drive wheels in one plane but it comes up with a rebuild error in the normal plane??

there are no restricting mates, and i am doing exactly as i am when it works.

Somebody please help!!

like i say im sure it is something very simple!