Out of Office Assistant not working

[Guest]

There's a problem in my office and it happens to some
users (not all, just few of them). The problem is, they
can't use Out of Office service.
I tried my user account and activate Out of Office on the
same PC and it works, but not to some other users accounts.
Is the problem on user profile or what?
We are using Exchange 5.5 and Outlook 2000.

Anyone has any idea about this?

Thanks