Hello Forum,
i had download Unity 3, Free Version and i had create cube as ground with a Mesh Collision and add by the Camera the Script: FPS Walker.
If i start the Game and try to Walk than i fall through the ground, the FPS Walker dont make a Collision with the Cube, i have the same problem by Rigidbodys too 
How can i make that Unity make by the FPS Walker and by the Rigidbodys the Collions again ?
Need help
Melone
meshes dont collide with meshes, meshes only collide with primitive colliders (sphere cube etc).
This is mainly because calculating collisions between meshes can get very expensive.
If you dont get good enough control with this, you can add any number of primitive colliders to your character.
By Unity 2.6.1 i can do this !
Almost all my colliders stopped working when I migrated to 3.0 – triggers, non-triggers, simple box colliders, everything. My player could only collide with a single mesh collider, but that working collider had a twin from the same .fbx file with the same collider settings and that wasn’t working. It seems like a bug to me (and it all worked in 2.6 just fine). I haven’t tried (put off migrating to U3), but you may need to recreate some of your colliders.
Unity is just a shit Engine !
Unity is the most powerful and usable game engine I’ve had the pleasure of getting my hands on, especially among free engines.
Perhaps you have simply set up your objects incorrectly. I am not currently having any issues with collisions.
I am currently experiencing a problem with Mesh Collider’s as well, and they were not a problem in 2.6.
I am noticing that on the object that has the mesh collider, if I turn ON a rigidbody, it works a bit better-- is this the case for you as well?