After I rendered my last picture I noticed some random "stars" errors all over the picture and I wonder where those come from. I am very sure these things are not part of the scene since they appear at different positions each time I render the image.

This never happend to me before so I am a bit confused.

It is known bug in the 3DeLight render engine when using Deep Shadow Maps for any of the standard lights in the scene in conjunction with UberEnvironment lighting.

I've noticed them from time to time too, mostly after a number of renders.  I find generally that closing down the program and trying again fixes the problem, so it may be tied to memory usage.