Thanks for the reply @martin
I am using my High School Hostel LAN Connection and also I check at that time my SN was not expired
The links say : "'Expired' - This means that the device did not activate with-in 24 hours after you added it. You can re-enable the device using that pop-up window and using the Re-Enable function. This will put the status back to 'Not Activated' and you'll need to trouble-shoot why it is not activating."
How to troubleshoot when it is not Activated???