Ubuntu – 15.04 can’t connect to password-protected Wifi

If the connect button is greyed out, your passphrase does not match the expected encryption standard.

For instance: WPA/2 passworts need to be between 8 and 64 Characters. If you have less characters in your passphrase, the connection Button will not activate.

It may happen that ubuntu does not correctly recognize your routers encryption. In this rare case you should edit your connections security to what your router is set to under Connections -> Wireless -> edit "Your connection" -> Security

I have been having similar issues (same wireless card). Here is what I did to fix it:

sudo service network-manager stop
gksudo gedit /etc/modprobe.d/iwlwifi.conf

Add options iwlwifi 11n_disable=1 to file, save, and close. Then:

sudo rmmod iwlmvm iwlwifi 
sudo modprobe iwlmvm iwlwifi 
sudo service network-manager restart

This will inactivate Wireless N so network speed may be affected.

If that doesn't work undo what you did by:

gksudo gedit /etc/modprobe.d/iwlwifi.conf

and delete the last line (options iwlwifi 11n_disable=1) and everything will be back to the way it was before.