Problem with mesh collider

Hello this is my mesh collider

40935-mesh1.png
And when i check Convex it makes this

Any solution?

Because your mesh is a concave mesh and you are setting it to be convex mesh so Unity generates convex colliders based off the shape of your mesh (your image 2).

Read: Convex and concave polygons for more details.

The problem is better explained in the video from this thread Concave Collider - Generate compound colliders with one click!. It is a forum thread for an asset that allows for concave mesh colliders.

This post states the same problem.

http://forum.unity3d.com/threads/resize-plane-object-mesh-collider.32128/

I guess the physics engine can’t figure out if your mesh is convex, since its not volumetric. Give it a height and I bet it works.