Render-Problem with Particles

Hey there,

I am a blender noob. I am just doing a little forest-scene (cycles, 2.7) in which I added three particle systems. One of them contains little bushes leaves with a translucent shader (not sure, weather that matters). In my renderpreview everything looks just fine. In the “real” render, I´ve got in the beginning just a black frame with some fireflies. Then I deleted the particlesystem - and the render was fine. If I then add another particlesystem with the same group of little bushes as particle, then - somehow - my background (a jpg) gets a weired structure and as well the particles are not the right verticies anymore. And somehow they´re too big as well. Is this because of some materials I used? Is it because of a corrupted file? Has anyone have any ideas?

thanks a lot in advance, and sorry for my bad english skills …

Soon I´ll add a few screenshots …

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