You know what? I had this problem too. During countless install/uninstalls/upgrades of statusbar-clock (Large Statusbar Clock) for development I never had this issue once.

I recently installed statusbarclock (single wide) just to check it out. Everything was fine, so I disabled it then uninstalled it. More recently I installed a testing version of Large Statusbar Clock (that is not available anywhere so can't be causing anyone's problems) and got this problem.

I fixed it the way burmashave suggested. However, it seems this method is not the complete story. As root, edit the file /usr/share/applications/hildon-status-bar/hildon-status-bar-battery.desktop and /usr/share/applications/hildon-status-bar/hildon-status-bar-internet.desktop and remove completely the "Mandatory=true" line. Now they should be selectable in the control panel.

Looking at the statusbarclock code, it seems to dispose of itself properly. I can't see any reason either of the applications would change both of the .desktop files mentioned above and the statusbar.conf file.

If anyone else has this problem, please weigh in about your usage of the two programs seemingly causing it.