Recurring Appointment: no error, not visible - exchange-server

Question

I am creating a recurring appointment via EWS managed API.
Creating Weekly appointments works.
Creating Monthly Appointments doesn't work.
When EWS posts my monthly appointment to the server, Exchange does not return any error, yet the appointment is not there.
All I can see, it should be there - but it isn't!
Does anyone here know why?
Here is the trace of the recurrence posted to the server:
<t:Recurrence>
<t:RelativeMonthlyRecurrence>
<t:Interval>1</t:Interval>
<t:DaysOfWeek>Saturday</t:DaysOfWeek>
<t:DayOfWeekIndex>Last</t:DayOfWeekIndex>
</t:RelativeMonthlyRecurrence>
<t:NumberedRecurrence> <br /> <t:StartDate>2014-04-26</t:StartDate>
<t:NumberOfOccurrences>10</t:NumberOfOccurrences>;
</t:NumberedRecurrence>
</t:Recurrence>
and here is the trace of the response header
<Trace Tag="EwsResponseHttpHeaders" Tid="18" Time="2014-04-25 14:00:56Z">
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Encoding: gzip
Vary: Accept-Encoding
X-EwsPerformanceData: RpcC=13;RpcL=919;LdapC=0;LdapL=0;
Persistent-Auth: true
Cache-Control: private
Content-Type: text/xml; charset=utf-8
Date: Fri, 25 Apr 2014 14:00:56 GMT
Server: Microsoft-IIS/7.5
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
</Trace>
and the response body.
<Trace Tag="EwsResponse" Tid="18" Time="2014-04-25 14:00:56Z" Version="15.00.0516.014"> <br /> <?xml version="1.0" encoding="utf-8"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<h:ServerVersionInfo MajorVersion="14" MinorVersion="0" MajorBuildNumber="722" MinorBuildNumber="0" Version="Exchange2010" xmlns:h="http://schemas.microsoft.com/exchange/services/2006/types" xmlns="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" />
</s:Header>
<s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<m:CreateItemResponse xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
<m:ResponseMessages>
<m:CreateItemResponseMessage ResponseClass="Success"> r /> <m:ResponseCode>NoError</m:ResponseCode>
<m:Items>
<t:CalendarItem>
<t:ItemId Id="AAMkADZmMGNlYzkwLWE0NGUtNGQxMC04MTc4LTE3MWM3MzExM2UzMQBGAAAAAAAVFLM1uwjxTpI7ZWapZLFDBwAG/DdYA3s2SJJPro446HsmAAAAAAAgAAAG/DdYA3s2SJJPro446HsmAAAOswdMAAA=" ChangeKey="DwAAABYAAAAG/DdYA3s2SJJPro446HsmAAAOsyvo" />
</t:CalendarItem>
</m:Items>
</m:CreateItemResponseMessage>
</m:ResponseMessages> r /> </m:CreateItemResponse>
</s:Body>
</s:Envelope>
</Trace>

Answer 1

Given that your XML is invalid, no surprise:
<t:DaysOfWeek>Saturday</t:DaysOfWeek>
^^^^---- should be just <
<t:DayOfWeekIndex>Last</t:DayOfWeekIndex>
^^^^----ditto
<t:NumberedRecurrence> <br /> <t:StartDate>2014-04-26</t:StartDate>
^^^^^^---huh? ^^^^----ditto