i've run into this issue multiple times in ubuntu while waking up from a suspend / hibernate like operation. right clicking on the Network Manager on the notification area shows 'Enable Wireless' but unclickable and in grey. you can fix this by making following changes to file:

/var/lib/NetworkManager/NetworkManager.state

and making sure it looks like:

[main]

NetworkingEnabled=true

WirelessEnabled=true

WWANEnabled=true

sometimes a "sudo service network-manager" is enough after the previous step to reflect the change, but on other occasions i've had to reboot my machine.

give this a try when you're stuck and let me know if it works.