Comment 4 for bug 779638

Now I realize the problem started to appear after I did the following, in order to re-enable the notification area (systray) in Ubuntu 11.04 for all applications:

"It's a new feature in Ubuntu 11.04 where the systray is only used by indicators and not regular applications. To overcome this, you can enter the following command in a terminal and then restart your sessions (log out and log back in): gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"."

http://www.webupd8.org/2011/04/how-to-re-enable-notification-area.html