Re: cannot compute backend DFP timings
You've set the ModeValidation option to reject every type of mode. I'm not sure why you're doing that, but its not a good way to debug the original problem.
However, according to the EDID in your display, you need a 162Mhz pixelclock to run with the native 1600x1200 mode. Your hardware isn't capable of that pixelclock:
(--) NVIDIA(0): ViewSonic VP201b (DFP-0): 112.0 MHz maximum pixel clock