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What if OWA stops responding?

Why it happens and how to fix it.

When a user accesses a given account on Exchange with Outlook 2003, and then uses Outlook Web access (OWA), the OWA service may stop responding. The reason for this lies in the way Outlook 2003 handles a certain MAPI property, PR_FREEBUSY_ENTRYIDS, which normally has only three entries. When OWA accesses this property it expects to find three entries, but Outlook 2003 adds a fourth entry to this property. OWA can experience heap corruption when it tries to read this fourth entry and can stop responding over time.

The problem is endemic across all versions of Exchange, but can manifest differently, depending on the version. For instance, in Exchange 2000 or Exchange 2003, a similar error can take place in the Collaborative Data Objects (CDO) component when the same MAPI property issue problem takes place -- so the corruption problem is not always limited to OWA itself. If you are experiencing problems with CDO in Exchange 2000 or Exchange 2003 and you are using OWA, consider this as a possible culprit.

Fixing the problem requires a different procedure for each version of Exchange:

Exchange 5.5:
A hotfix for this problem is available specifically for Exchange 5.5, which can be downloaded from Microsoft at

Exchange 2000:
Apply the September 2003 edition of the Exchange 2000 Server Post-Service Pack 3 (SP3) Rollup to fix this problem which can be found here:

Exchange 2003:
A hotfix for Exchange 2003 is available from Microsoft here: (Odds are this hotfix will be superseded by a future Service Pack for Exchange 2003.)

In all cases it is a good idea to reboot the Exchange server after applying the hotfix.

Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter. Check out his Windows 2000 blog for his latest advice and musings on the world of Windows network administrators -- please share your thoughts as well!

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