Wi-Fi disabled and greyed out after iOS 6 update on the iPad or iPhone

My Iphone 4s sunddenly got the same problem wifi get grayed/option disabled. I have IOS 6.1.2 then i tried to reset it airplane mode on/off but the same. So please guide me what i have to do?

Several users have reported Wi-Fi problems after updating to iOS 6. Mostly users have reported that the Wi-Fi option was greyed out.

It seems that this bug was a result of Apple’s servers being down for a short time. It has been further reported that this bug was fixed by Apple, so you do not need to do anything. If you are still having this issue, please leave a comment here.

UPDATE

It seems that many users are still having this problem.

Possible fixes:

Reset network settings (General->Reset->Reset Network Settings)

Toggle Airplane Mode on/off

Restart your device

Turn off Cellular Data ( Settings > General > Cellular) then try to connect to your WiFi.