Error message when you try to add a delegate in Outlook 2007: "The Delegates settings were not saved correctly"

When you try to add a delegate to the mailbox of another user in Microsoft Office Outlook 2007, the delegate is not added. Additionally, you receive the following error message:
The Delegates settings were not saved correctly. Unable to activate send-on-behalf-of list. You do not have sufficient permission to perform this operation on this object. This issue occurs when the global catalog to which you are connected is not writable to the current user.

http://support.microsoft.com/kb/950794