Outlook 2003, Exchange 2003

Before creating a public contacts folder when clicking on "Open a Shared
Calendar" in Calendar the resulting dialog offered a choice of Users. Now
the same click only offers a choice of Contacts. This occured on two
workstations being setup exactly the same way.
Surely something must be wrong, else how do you now select a user who has
shared their calendar?
In addition on clicking "Share My Calendar" the calendar properties window
opens.
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Clyde