How to render a scene with Cycles render and blender internal My problem is that I have made a in Blender render a plane with grass texture and I have made some rocks in a separate blender file with Cycles render. The problem is that when I do BR then it renders only the plane and the rocks are plain grey and when I do CR then the plane is grey but the rocks are looking good. Hopefully somebody can help me quick how to solve this issue

The video I used to do the rocks:
https://www.youtube.com/watch?v=xRDFMYfsIcU
The reason why you get gray a plane or rocks, is that materials are different in BI and Cycles, so to use, let's say Cycles, you have to "port" your materials (basicly remake them, with the tools availiable in the render engine); Since materials are different, when you switch between the renderers it applys a default materail to objects that don't have a propper one; That material just so happens to be gray. 
So I don't think it's possible to mix them, without using the compositor and transparency.