Out of Office does not function

We are running Exchange 5.5 with Outlook 2000 clients. When invoking the Out of Office Assistant, all options are available and it turns on. Nothing else happens, i.e. no auto responses are sent. Am I missing something, or not configuring something else, or do I have a problem on the Server. This does not work for internal e-mails or external. Yes I enabled this in the IMC, but could find no other place to set it.