Meetings are unexpectedly moved one hour ahead in the last week of October 2006 in Exchange Server 2003

Published Oct 20 2006 01:38 PM 1,227 Views

Seeing that we have seen some support calls on this already, we wanted to highlight a KB article that was written about the above mentioned issue. The article in question is:

Meetings are unexpectedly moved one hour ahead in the last week of October in Exchange Server 2003

Here's a little FAQ on this:

1. Where do I need to put this fix?
You need to put it on the machines where CDO applications run. See http://support.microsoft.com/default.aspx?scid=kb;EN-US;917481 for more details.

2. Is OWA affected?
Yes. CDO is used for free/busy information so there could be some impact here.

3. What about Outlook clients?
Outlook does not use CDO for creating appointments, but if the appointment was created by CDO for next week then it could show incorrectly in Outlook.

4. Will the problem happen next year?
No. The reason this is happening is because the transition that is hard coded into CDO for the DST transition for GMT is incorrect. The transition in CDO is coded for the 4th Sunday in October and in most years this is also the LAST Sunday in October, which is the correct day for the transition. However, in 2005 and 2006 there were 5 Sundays in October so the transition date in CDO was incorrect which results in some appointments being 1 hour out. This problem will disappear once DST ends on the 29th October. The next time this issue will happen is 2010.

5. I am in XYZ timezone, will this affect me?
Only if you are using CDO to schedule meeting requests in the GMT timezone, then you could be affected. Please check the KB to see if your timezone has had a fix to it.

6. What hotfixes are available for this issue?
Exchange 2003 POST SP2 - http://support.microsoft.com/default.aspx?scid=kb;EN-US;910268
(there is no post SP1 fix for this. SP2 has been out for nearly a year now!)

Exchange 2000 - http://support.microsoft.com/kb/888606
Exchange 5.5 fix here - http://support.microsoft.com/kb/837010

7. What about appointments already created?
Preliminary reports suggest that one-off appointments created using CDO will be incorrect next week, recurring appointments with an occurrence next week will be out for next week only but recurring appointments starting from next week will be one hour off for all occurrences.

Thanks to Jonathan Unwin for help in creating this FAQ!

- Paul Flaherty

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