Originally Posted by Xophile
Your card does not support it as it only has one RAMDAC
This turns out not to be the case. All consumer GeForce GPUs since GF2 MX have two usable integrated RAMDACs, excluding the GF3.
I know this because when I worked at NVIDIA, I wrote/edited NV17/18 (GF4 MX) datasheets. I recall the NV18 DAC configuration specifically, because the original analog section differed from previous GPUs. However, the released version has two usable DACs.
However, Xophile may be partially correct: your card probably fails to support nView and cloing because only one RAMDAC is shared between TV and VGA. From your brief post, it appears the VGA and the TV output were not designed to use separate DACs, and so cannot be used simultaneously. This is an OEM design choice, not a limitation of the NVIDIA chip.
Who is the OEM manufacturer of your card (ASUS, MSI, etc)?
What version of the drivers are you using?