Mesh changes its shape in game engine I'm learning to use the game engine and I don't know why a mesh change its shape when I press P key.

This happened when I subdivided the red mesh. I subdivided it because I want the ball collide the red wall but I don't want a rigid wall, I want a soft wall. 




Here is the file: http://www.pasteall.org/blend/28811
(The ball moves with left and right arrows)

Thank you!
This is because you modified the mesh in some way after changing the physics Type. To fix, just simply apply the scale on the object, you can quickly do this with CtrlA > Scale or from the 3d view header choose Object > Apply > Scale.