Ubuntu - How to resume NetworkManager managing network interface

After manually editing /etc/network/interfaces for dynamically assigned IP or static IP, Network Manager (the icon sits on the upper panel with 2 monitor) stops working. Specifically it stop managing interface, but manually assigning IP through "ifconfig" or editing config files (/etc/network/interfaces) still works. Another reason NetworkManager stop working is after applying some updates between Intrepid (8.10) to Jaunty (9.04) it just stop working. Here is the solution :

1. Replace all the contents in /etc/network/interfaces with :

auto lo
iface lo inet loopback

2. Make NetworkManager resume managing the network interface :

sudo vi /etc/NetworkManager/nm-system-settings.conf

and make sure the parameter "managed" is set to "true".

e.g.

[ifupdown]
managed=false

change to

[ifupdown]
managed=true

3. Kill all existing process (to clear the old behavior) :

sudo killall nm-system-settings

4. Restart NetworkManager by :

/etc/init.d/NetworkManager restart

Voilla !!!