I use the AppointmentCalendarExporter behind a WCF service to produce an ICal stream. This is then imported as a subscription to Outlook.
When an appointment has a recurrence pattern that is every 2 days (See the attached example). it produces the following output (just for that appointment)
DTSTART;TZID=E. Australia Standard Time:20111225T050000
DTEND;TZID=E. Australia Standard Time:20111225T120000
However, this can't be imported into Outlook. There is a conflict in the recurrence rule, between FREQ and BYDAY. If I remove the BYDAY, then it gets imported ok.
I think this is a bug.