FYI, in Ubuntu 12.04.1 there is a bug with Network Manager (also used in Xubuntu I believe). After a while the Network Manager applet will kind of turn into a zombie; VPN menus won't expand, extra wireless networks won't show, etc. I believe this was supposed to have been fixed in 12.04.2, can't verify that myself.
The way I fix this is crude but it works: kill the nm-applet process and restart it. In a terminal:
which produces - for example:
ps -afe | grep nm-applet
The process number in my case is 3237. Kill the process:
username 3237 3126 0 Mar19 ? 00:00:17 nm-applet
Then start a new nm-applet: