Comment 15 for bug 1158432

I've found a couple of workarounds:

1) Navigate to the /etc/NetworkManager/system-connections folder (as superuser)
2) Open the file that is named after the wi-fi network your computer tries to autoconnect at startup
3) Use a text editor to remove a line called "password-mode=1" (or something like that)
4) Your file should look like this: http://askubuntu.com/a/354986

or

1) When the computer is booting, turn off the physical network switch. Turn in back on after you log in.

or

1) Try wicd instead of the buggy NetworkManager.