'Activation of wireless network connection failed' error with a BSNL BroadBand modem# DNA-A211-I
Install wicd network manager. It should work. It's available in Ubuntu software Center.
Its all in the signal strength. The Network Manager would oscillate around -28db to 70db (meaning a large fluctuation). And with Wicked (WICD), it's around a -70 tops.
I would recommend to install EtherApe or WireShark to analyze your network connection.
sudo apt-get install wireshark
sudo apt-get install etherape