I have been working on the scene for the last few weeks, I have done a quick experiment with a camera following the path and since then Blender won't render from any camera, unless it's set to CPU. I have a really good graphics card and there were no problems with rendering with GPU at all before I set this camera to follow the path. It seemed to mess some settings up... When I try to render in a GPU mode it only shows the blank grid (screenshot attached).
It takes it about 40 seconds, then it stops rendering, the screenshot 2 message shows in the top window and the image stays blank. Another thing that has changed since I've made a camera follow the path are the transform settings, they were green, then I must have done something and they're not green anymore.
Hope it all makes sense!