I had the same problem, wireless network would ask for a password to authenticate, then connect and after a couple of seconds it would disconnect again. This process would repeat itself over and over. Even with entering the password directly at the wireless security tab as described here, it would still pop-up with the password dialog box & sometimes connect, but still keep on disconnecting.
This is what I did to solve the problem - it's a workaround, but hopefully later updates will fix this issue.
- Establish a connection to your wireless connection
- Click on the network icon at the top right-hand of your screen
- Select 'Edit Connections' at the bottom
- Select the 'Wireless' tab
- Select your network & hit 'Edit'
- Select the 'IPv6 Settings' tab
- Where it says 'Method: Automatic' make it 'Ignore'
That "solved" the problem for me, of course it potentially creates other issues if you need IPv6 on your wireless connection, and hopefully that gets resolved later with updates from Ubuntu or upstream.