The Activities page shows activities only in certain folders, the folders defined in the various "activity groups," which are managed from the Properties dialog on the contacts folder. Your symptoms suggest that either you're working with a journal folder that isn't included in the activity group you're looking at or (maybe more likely), the activity group is corrupted. Try creating a new activity group that includes the desired folders.
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers