2D Collider stucking with each other in unity 2D toolkit?

I’m using 2d collider and they are stuking some time with each other, as shown in the image ball is inside a box. Does anyone having solurion or any suggestion for this problem?

[21450-screen+shot+2014-01-31+at+2.41.59+pm.png|21450]

Recheck the position of both the collider i.e. ball and crate and also check if is triggered is not selected.