Objects cloning on movement?

I can’t be more specific more than posting this picture. Everything was working fine until I closed the project and opened it again (I didn’t change anything). This was the result when I ran the game…

[19918-screenhunter_39+dec.+30+12.22.jpg|19918]

Basically what happens is that the cube moves by mouse movements and when the cube moves it leaves a stream of copies of it. That planet shoots another cube and the same thing is happening.

Can someone explain to me what is happening and how I can get rid of this?

Check your camera object that is rendering this view and make sure clear flags is set to skybox. This is what you get when you set it to depth only.