Network icon disabled in ubuntu 11.10/12.04

Firstly, stop the network manager service by typing in terminal:

sudo service network-manager stop



Open nautilus in sudo mode by typing in terminal:

sudo nautilus
    
Goto etc/NetworkManager and open  NetworkManager.conf.

Change the managed value to true:


Restart the Network Manger service by typing in:

sudo service network-manager start

And after that your Network Manger should be back online.

Source: http://solancer.blogspot.in/2011/10/network-icon-disappeared-in-ubuntu-1110.html