Textures with Mix Shader won't get rendered

Hey folks,

I’m still a beginner at blender and currently doing a book animation for a small film we have to do for university. I followed a lot of tutorials to do this and was able to solve all occuring problems by myself, but now that I’m an inch away from finishing I’m just not getting it done.

I’m animating a book with pictures in it which has some of the pages flipping. For the down laying mass of pages I just assigned the book page texture with the photo texture node and everything’s working fine. For the flipping pages I followed a few tutorials to get them double-sided using two image textures and a mix-shader with the geometry- backfacing-node assigned to it. And while the pages just with the texture node are working perfectly, the ones with the mix shader aren’t. The textures get shown when I switch the display mode to Materials or Textures, but they won’t when I switch to render mode, the pages are just shown white.
I tried everything that came to my mind by now but I’m just not getting why the textures are not showing and it’s really driving me crazy right now.
I hope some of you guys can help me solving this. :slight_smile:

(I wanted to attach my blend-file but the uploader kepps saying that it failed the upload so you’re finding it here, I’m sorry: http://www [dot] filedropper [dot] com/snowgard-book-notrendering )