Having trouble with a render

Hello Fellow artists,

I am working on an attempt at realism and I am having trouble with two things in my render. First if I turn on volume scatter, under the world settings, and render it completely removes the HDR that I am using in my scene. Does anyone know why? Second is a two fold problem, I had tried rendering the piece out and got an error saying that there wasnt enough memory designated for the CUDA cores. This didnt make any sense to me because my machine should be more then sufficient to render this. So I set the dimensions and passes lower and it rendered but it only gives me a blank PNG. If I render it out with my CPU it works fine, but the GPU wont work. Can someone please help me to figure out what I may have done wrong with my set up?

Attachments

RealismDesk.blend (2.73 MB)

First if I turn on volume scatter, under the world settings, and render it completely removes the HDR that I am using in my scene. Does anyone know why?
See https://cgcookie.com/blender/lessons/cycles-volumetrics-world/

Second is a two fold problem, I had tried rendering the piece out and got an error saying that there wasnt enough memory designated for the CUDA cores.
Does your graphics card have sufficient memory to hold your whole scene