This happens every time I go to add a Rigidbody component. To reproduce this, I have follwed the Roll a Ball tutorial, second lesson. When I go to add a Rigidbody component to the Player object, Unity3d crashes. I have done this multiple times to reproduce, and it happens every time. To bypass this issue, after adding a Rigidbody component, I quickly save the scene. And after it crashes, I restart Unity, and everything is fine.

It happens to me too but only for the first time after restart everything is ok.