Comment 2 for bug 466568

Try checking /var/log/daemon.log when attempting to connect to an Ad-Hoc network. I suspect you may see something like this:

Nov 18 08:57:20 novosirj-laptop NetworkManager: <WARN>
> >>>> wait_for_connection_expired(): Connection (2)
> >>>> /org/freedesktop/NetworkManagerSettings/2 failed to activate (timeout):
> >>>> (0) Connection was not provided by any settings service

If that is the case, this appears to be the bug we're both being affected by. I spoke to one of the Network Maanger maintainers and what he said was:

So this log indicates that the applet isn't creating the connection correctly and providing it to NetworkManager after you click the
network.

Can you confirm that you see the same log entries?