updateItem no attendees!

--> POST https://exchange.dataart.com/EWS/Exchange.asmx http/1.1
Content-Type: text/xml;charset=utf-8
Content-Length: 1367
SOAPAction: http://schemas.microsoft.com/exchange/services/2006/messages/UpdateItem
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange
   <soap:Header>
      <t:RequestServerVersion Version="Exchange2010_SP1"/>
      <t:TimeZoneContext>
         <t:TimeZoneDefinition Id="Pacific Standard Time"/>
      </t:TimeZoneContext>
   </soap:Header>
   <soap:Body>
      <m:UpdateItem ConflictResolution="AlwaysOverwrite" MessageDisposition="SaveOnly" SendMeetingInvitationsOrCancellations="SendToAllAndSaveCopy">
         <m:ItemChanges>
            <t:ItemChange>
               <t:ItemId Id="AAMkAGRjMzNmZmY5LWU3MGQtNDM3Yy04NzhkLTIwMTg1NmFhMGQwNABGAAAAAABObYYk+7J4Q7aaFHkkbfVkBwDfWJVQrwZNRp/OY9bjrUjZAAAAfj7xAAB+MrFosgBHQqrkDt0N/PWCAALNcd9DAAA=" ChangeKey="DwAAABYAAABMdkyja/VqSJV6H6Cs0yfEAAByxN63"/>
               <t:Updates>
                  <t:SetItemField>
                     <t:FieldURI FieldURI="item:Subject"/>
                     <t:CalendarItem>
                        <t:Subject>Kirill Varivoda Meeting1</t:Subject>
                     </t:CalendarItem>
                  </t:SetItemField>
               </t:Updates>
            </t:ItemChange>
         </m:ItemChanges>
      </m:UpdateItem>
   </soap:Body>
</soap:Envelope>