OS X El Capitan "Install for all users of this computer" greyed out?

Hello guys,
Yesterday I downloaded El Capitan on my 15" Macbook Pro. My internal wireless receiver is broken and I must use external USB. I was trying to install the driver for the USB "Netis WF2111" and I kept getting stuck in the installation wizard. When I was supposed to continue it wouldn't let me.
Note: I erase my Mac to factory reset and tried again but it kept showing me the same thing. From settings I have enabled installing apps form Anywhere. Also tried to install it from another user but same thing shows up. Any ideas?
Thanks!

Update: Another note: I used the USB before I upgraded and it worked well.