Outlook 2002, very similar problem, might be your issue too.
It appeared that I had the same problem. It started happening yesterday
right after I tried to archive a bunch of stuff to get the sys admin mail bot
to stop telling me my mailbox was too large. All of a sudden, it appeared
that EVERY calendar entry disappeared!
FINALLY, I realized that I was trying to view my calendar entries in the
calendar folder within my Archived Folders and not my Outlook Today folders.
Once I selected the correct calendar folder, I saw that everything was there,
as expected.
Turns out I am the DEFINITION of User Error.