I had exactly the sqme problem as you...
Now it works, the origin of th problem was that one of the monitor was bad configured.
To fix it I run an XF86Config with only one screenm device and monitor. and selecting the external CRT and LCD by the Fn+CRT/LCD keys.
I autodetected the monitor type and frequencies for each of them and write both settings of the two monitors.
After that I checked the XF86Config and putted the right settings, now it works!!
I've noticed you have 1600x1200 as higher resolution of your LCD.
Maybe if you adjust both to a lower resolution it work directly just try 1024x768 as maximum in both screen sections (my panel in a Dell 8200 is 1450x1050) surely your fail is there because you have copied that from the Nvidia Text file.