We had this last week, caused by a user bombing out of Outlook. They thought it had crashed when in fact they were mailing a 100Mb file to someone.<br>
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Kind of a frig, but it worked for us:<br>
Kill the store.exe process.<br>
Stop the Exchange services.<br>
Set Exchange services to manual.<br>
Restart server.<br>
Install NT SP5 then Ex SP2 (hope you are using 5.5 cos I don't know about 5.0).<br>
Re set Exchange services to automatic.<br>
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This worked for me.<br>