Problem with Object collision

Hi everyone,

I imported a mesh and auto-generated colliders for it.
For now I dont mind at speed or FPS, it should just work. But it dont work.
I want my Object to collide. I justed the drag rigidbody script.

The obect consist of several chilc objects, collision works, but just with the ground, the the child objects itself does not collide to each other.
They all got mesh colliders, and they all got rigidbodys (even with continues dynamic collision!)
It wont work!
So what im doing wrong?

MeshColliders will only collide with each other if set to convex.