User switcher applet crashed, deleted in Ubuntu

I don't know why it happened to me. I am still in Ubuntu 10.04. Last time when I start my machine, after desktop appear this message showing its nose to me. It says:

The panel encountered a problem while loading "QAFIID:GNOME_FastUserSwitchApplet".

I delete it. So 'Me Menu' also disappear from my Ubuntu machine. I thought deleting a crashed application is better. Later, I have searched my Ubuntu system and even in Google but failed to recover/ reinstall it. I did not find the way to get it back anywhere. I found this page by Google search result, but there is no any solution or download for Ubuntu 10.04.