Render Problems FLickering

Dear all
I experience lots of flickering in the background as you can see in the background. In the scene I use a Fastnoise to make the blue nebula and map it on a big sphere. The camera movement is an imported camera from a c4d scene via fbx. The black background is posted after the 3dmerge node in a 2d merge. The flickering looks like polygons that don´t know texture they have ...
Any ideas what that could be??

Thanks in advance for your help.
Cheers

Problem solved!
I decreased the z-range of the camera to 1 to 600 and the polygonal flickering was gone...

Martin