Comment 46 for bug 1542733

Just to confirm, for me the problem is fixed if you have downloaded the latest ISO version 16.04.2, installed the operating system, then once installed you MUST manually run the Software Updater & do all the updates & reboot. Unfortunately ticking the box during the installation to say do the updates during the install isn't enough!! You'll find then that the Hidden Wireless Network isn't greyed out.

It's just a shame the update wasn't applied before the 16.04.2 ISO release because at the moment if you install & don't do the full updates you will have the problem. It's annoying too because during the installation of the operating system if you've connected to your Wifi then reboot, it will be greyed out because you haven't had the chance to run the software updater ... When that happens to save time I click on the network connections applet & select edit network connections, then under Wifi delete my initial Wifi connection I made during the install, close it & make a new connection to my Wifi & do all the updates via Software Updater.

This will be fixed by the time 16.04.3 is released but that's a while down track which is why I was hoping the patch was done before 16.04.2 ISO was released but it just missed out...

The only thing I don't know is what Christopher rightly mentioned on #43 is if you installed Ubuntu from either ISO version 16.04 or 16.04.1 & you have done all the updates if the problem is fixed.. For me I only install Ubuntu LTE version from .2 onwards because it has the rolling kernel release for newer hardware (HWE) which I prefer personally but if people choose to use the fixed linux kernel version 4.4 which is under either ISO version 16.04 or 16.04.1 then thats fine but someone will need to test.
I've done at least half a dozen machines using the 16.04.2 ISO & using the procedure above it's fine but as mentioned just annoying.. Sorry for the long comment..