Cannot view contacts or calendar in offline mode

I'm sure this is simple but I can't seem to find the answer. A few of our
users cannot seem to access their personal contacts or calendar appointments
when using Outlook in offline mode. This occurs with both various versions of
Outlook including 2003. We are running Exchange Server 2003 and Windows XP is
the operating system. I have set up offline folders for each of these
machines and they do routinely synchronize using Send and Receive. The
personal contacts and calendar appointments were upload to Exchange via a PST
file. They can see the contacts and appointments just fine when they're
running in online mode.

Any help is appreciated!