UPDATE: We have now released the hotfix that corrects this issue for Exchange 2003 SP2. The article is:

930241  The Exchange 2003 database does not mount, and event IDs 9518 and 9519 are logged in the Application log
http://support.microsoft.com/default.aspx?scid=kb;EN-US;930241

The hotfix can be downloaded from here:

http://www.microsoft.com/downloads/details.aspx?FamilyId=2A835A09-8E57-4027-A488-1E61C4B43A10&displaylang=en

For anyone who has used the workaround outlined in:

932599  Information Store database does not mount with Event ID 9519 and 9518
http://support.microsoft.com/default.aspx?scid=kb;EN-US;932599

You can apply the hotfix from 930241 and revert your permissions back to how they were before the application of the DST fix and the implementation of the workaround.

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As everyone in the US IT industry is now aware, there will shortly be a change to Daylight Saving Time here in the US. DST will be starting three weeks earlier and ending one week later. So in order to accommodate this change Microsoft has released a number of hotfixes both for windows and for various Microsoft applications that are affected by this change. One such fix is the CDO DST update for Exchange 2003:

Update for daylight saving time changes in 2007 for Exchange 2003 Service Pack 2
http://support.microsoft.com/kb/926666

In Exchange 2003 (as was the case with all previous version of Exchange) any new hotfixes that are released contain all previous hotfixes. This is because Exchange fixes are built on top of each other to ensure that we don't have hundreds of "special" version of Exchange components; and that all pieces of the product will continue to work properly. The side effect of this is that when a major fix comes out like the DST fix our customers may end up having some unexpected changes to their systems if they have not been keeping up with server hotfixes.

In the case of the 926666 fix, there are two primary issues that our customers are running into.

First, the DST fix includes a previous fix to the Send As behavior of Exchange 2003. The Send As behavior was changed in Exchange 2003 to move it to a more secure model when it was determined that the current model allowed for unexpected levels of access based on permissions assigned. To check if you are going to be affected by this change you should locate Store.exe in your "Exchsrvr\bin" directory. If the Version is lower than 7650.23 then when you apply the DST fix you will need to be concerned with the Send As behavior change.

The following articles document the Send As changes and what you will need to do to adjust for it much better than I can do here:

New Exchange fixes may disrupt Blackberry, Goodlink and other services
http://msexchangeteam.com/archive/2006/04/28/426707.aspx

"Send As" permission behavior change in Exchange 2003
http://support.microsoft.com/kb/895949/

Users cannot send e-mail messages from a mobile device or from a shared mailbox in Exchange 2000 Server and in Exchange Server 2003
http://support.microsoft.com/kb/912918

The other problem that you might encounter after applying the 926666 DST fix is that your database might not mount and generate an error when trying to mount. You will see events 9519 and 9518 with error codes 0x89a in the application log on the server. This is caused by a previous unrelated fix that was made for Exchange 2003. The above update to this post has the hotfix information. 

In the short term, we have published a public KB article that describes this store mount issue and provides a work around that should work for the vast majority of customers that are affected by this problem:

932599 Information Store database does not mount with Event ID 9519 and 9518
http://support.microsoft.com/default.aspx?scid=kb;EN-US;932599

Over all it is in your best interest to apply the DST fix for Exchange 2003 sooner rather than later. The sooner you get it on your system the less "fix up" will be needed of existing appointments.

For More information on the DST changes in please see:

Daylight Saving Time Help and Support Center
http://support.microsoft.com/gp/cp_dst

- Matthew Byrd