Office Assistant in Outlook 98

Out of office assistant and rules wizard are not working. Outlook 98 allows you to set up a rule or out of office message and turn them on, but when you send an e-mail to that PC, the rules do not respond and no out of office message is received. There is nothing on the server that seems to be causing the problem and Outlook has been set up exactly the same through out the company, but this seems only to effect some machines. Any ideas would be gratefully received as this is becoming a real nightmare!!