Outlook: Reversing Navigation-Pane Customizations

I opened a calendar folder from another user's mailbox in Microsoft Office Outlook 2003 and somehow managed to remove it from the Other Calendars list. Now, I can't get it back or it comes back but with no label at the top of the screen to tell me whose calendar it is. How can I fix this problem?

I've seen several variations on this problem with the new Outlook 2003 interface. The one sure solution I've found is to create a new Outlook profile. Surprisingly, what doesn't work is resetting the navigation pane by starting Outlook with the /resetnavpane switch. That action resets the navigation pane (reversing most navigation-pane customizations), but it doesn't fix the calendars.