I am having the same problem and followed the wiki's instructions for debug output... Here is what I got

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

getInterfaces called

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: adding item

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: queueRequest

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: setup req to https://LDS\<email address hidden>/EWS/Exchange.asmx user LDS\torgersondl

getInterfaces called

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: Sending: <?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages">
  <soap:Header>
    <t:RequestServerVersion Version="Exchange2007_SP1"/>
  </soap:Header>
  <soap:Body>
    <m:CreateItem SendMeetingInvitations="SendToNone">
      <m:SavedItemFolderId>
        <t:DistinguishedFolderId Id="calendar"/>
      </m:SavedItemFolderId>
      <m:Items>
        <t:CalendarItem>
          <t:Subject>CCNA class part 2</t:Subject>
          <t:Body BodyType="Text"/>
          <t:ReminderIsSet>true</t:ReminderIsSet>
          <t:ReminderMinutesBeforeStart>-345</t:ReminderMinutesBeforeStart>
          <t:ExtendedProperty>
            <t:ExtendedFieldURI DistinguishedPropertySetId="Common" PropertyId="34144" PropertyType="SystemTime"/>
            <t:Value>2011-05-23T05:45:00Z</t:Value>
          </t:ExtendedProperty>
          <t:UID>56e1228d-a421-452b-9e73-03db5bd3b32e</t:UID>
          <t:Start>2011-05-23T00:00:00-00:00</t:Start>
          <t:End>2011-05-28T00:00:00-00:00</t:End>
          <t:IsAllDayEvent>true</t:IsAllDayEvent>
          <t:Location>West Vally - New Horizons</t:Location>
          <t:RequiredAttendees>
            <t:Attendee>
              <t:Mailbox>
                <t:Name>Michael Buck</t:Name>
                <t:EmailAddress><email address hidden></t:EmailAddress>
              </t:Mailbox>
              <t:ResponseType>Unknown</t:ResponseType>
            </t:Attendee>
            <t:Attendee>
              <t:Mailbox>
                <t:Name/>
                <t:EmailAddress><email address hidden></t:EmailAddress>
              </t:Mailbox>
              <t:ResponseType>Accept</t:ResponseType>
            </t:Attendee>
          </t:RequiredAttendees>
        </t:CalendarItem>
      </m:Items>
    </m:CreateItem>
  </soap:Body>
</soap:Envelope>

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: getInterface

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: IID: {d974c99e-4148-4df9-8d98-de834a2f6462}

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: reply

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Body>
    <s:Fault>
      <faultcode xmlns:a="http://schemas.microsoft.com/exchange/services/2006/types">a:ErrorSchemaValidation</faultcode>
      <faultstring xml:lang="en-US">The request failed schema validation: The 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStart' element is invalid - The value '-345' is invalid according to its datatype 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStartType' - The value '-345' is not valid according to any of the memberTypes of the union.</faultstring>
      <detail>
        <e:ResponseCode xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">ErrorSchemaValidation</e:ResponseCode>
        <e:Message xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">The request failed schema validation.</e:Message>
        <t:MessageXml xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
          <t:LineNumber>16</t:LineNumber>
          <t:LinePosition>47</t:LinePosition>
          <t:Violation>The 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStart' element is invalid - The value '-345' is invalid according to its datatype 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStartType' - The value '-345' is not valid according to any of the memberTypes of the union.</t:Violation>
        </t:MessageXml>
      </detail>
    </s:Fault>
  </s:Body>
</s:Envelope>

ccd67502-4c01-4133-8952-e11d83a96573/Exchange: fail status: 500 <?xml version="1.0" encoding="utf-8"?><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Body><s:Fault><faultcode xmlns:a="http://schemas.microsoft.com/exchange/services/2006/types">a:ErrorSchemaValidation</faultcode><faultstring xml:lang="en-US">The request failed schema validation: The 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStart' element is invalid - The value '-345' is invalid according to its datatype 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStartType' - The value '-345' is not valid according to any of the memberTypes of the union.</faultstring><detail><e:ResponseCode xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">ErrorSchemaValidation</e:ResponseCode><e:Message xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">The request failed schema validation.</e:Message><t:MessageXml xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"><t:LineNumber>16</t:LineNumber><t:LinePosition>47</t:LinePosition><t:Violation>The 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStart' element is invalid - The value '-345' is invalid according to its datatype 'http://schemas.microsoft.com/exchange/services/2006/types:ReminderMinutesBeforeStartType' - The value '-345' is not valid according to any of the memberTypes of the union.</t:Violation></t:MessageXml></detail></s:Fault></s:Body></s:Envelope>

getInterfaces called

getInterfaces called


It appears that it has to do with the 'ReminderMinutesBeforeStartType' being less than 0.