When you have million+ polys maya tends to become unstable. If you absolutely have to have such a dense mesh try freeing as much memory as you can and use batch render (make sure to close maya after you start it or use the command line). Batch render is more stable.

However, it seems like your mesh would look fine with like 1/4 of the number of polys you have now. Try following Dann's advice. Also, turn on "Optimize" under "Mesh" in RF. This will create a dense mesh in areas that need more detail and less dense in areas that do not.