nvidia install application has stopped working

[salman2401]

I am trying to Install Nvidia Software so that I may switch in between Nvidia and Intel HD graphics.
I have Following :

Lenovo T420s
Nvidia Nvs 4200m
Intel Hd . Intel Core i7
Windows 7

Problem is that my device manager shows that i have Nvidia 4200m installed on my device meaning thereby its drivers are installed. However whenever I run the installation software windows generates error and stops in the midst of installation.
I am attaching image: http://imgur.com/ImfKSR3

 

[Phillip Corcoran]

Why are you trying to install a driver that's already installed?

And where did you get the driver from anyway?