XMLWriter output port problem - Output port is not connected

Somehow i am not able to use the result (xml) of the XMLWriter as input for the HTTP_CONNECTOR.
When i use fileURL="port:$0.XMLString:discrete" then i get the following message:

ERROR [WatchDog] - Graph execution finished with error
ERROR [WatchDog] - Node EXT_XML_WRITER0 finished with status: ERROR caused by: Output port is not connected.
ERROR [WatchDog] - Node EXT_XML_WRITER0 error details:
Output port is not connected.

When i use fileURL="-" then i see the correct xml output in my console. Even writing to a file works fine.

This is my code:

<?xml version="1.0" encoding="UTF-8"?>
<Graph author="rvloon" created="Mon Aug 29 13:27:09 CEST 2011" guiVersion="3.1.0" id="1314689455495" licenseCode="CLP1DAON37256641BY" licenseType="Commercial Pro" modified="Tue Aug 30 12:14:09 CEST 2011" modifiedBy="rvloon" name="Pacos" revision="1.40" showComponentDetails="true">
<Global>
<Metadata id="Metadata0" previewAttachmentCharset="ISO-8859-1">
<Record name="getAdres" previewAttachmentCharset="ISO-8859-1" recordDelimiter="\r\n" type="delimited">
<Field delimiter="|" name="postcode" type="string"/>
<Field name="huisnummer" type="integer"/>
</Record>
</Metadata>
<Metadata id="Metadata1" previewAttachment="${DATAIN_DIR}/pacos-request-pacos.xml" previewAttachmentCharset="ISO-8859-1">
<Record name="pacosRequestXMLData" previewAttachment="${DATAIN_DIR}/pacos-request-pacos.xml" previewAttachmentCharset="ISO-8859-1" type="delimited">
<Field eofAsDelimiter="true" name="XMLString" type="string"/>
</Record>
</Metadata>
<Metadata id="Metadata3" previewAttachmentCharset="ISO-8859-1">
<Record name="pacosResponseXMLData" previewAttachmentCharset="ISO-8859-1" type="delimited">
<Field eofAsDelimiter="true" name="XMLString" type="string"/>
</Record>
</Metadata>
<Metadata id="Metadata2" previewAttachment="${DATAIN_DIR}/pacos-request-pacos.xml" previewAttachmentCharset="ISO-8859-1">
<Record name="XMLData" previewAttachment="${DATAIN_DIR}/pacos-request-pacos.xml" previewAttachmentCharset="ISO-8859-1" recordDelimiter="\r\n" type="delimited">
<Field name="XMLString" type="string"/>
</Record>
</Metadata>
<Property fileURL="workspace.prm" id="GraphParameter0"/>
<Dictionary/>
</Global>
<Phase number="0">
<Node enabled="enabled" fileURL="port:$0.XMLString:discrete" guiHeight="87" guiName="XMLWriter" guiWidth="128" guiX="418" guiY="175" id="EXT_XML_WRITER0" passThroughInputPort="0" passThroughOutputPort="0" type="EXT_XML_WRITER" xmlSchemaURL="${DATAIN_DIR}/pacos-request-pacos.xsd">
<attr name="mapping"><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:clover="http://www.cloveretl.com/ns/xmlmapping" xmlns:adr="AdresGegevens" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Header/>
  <soapenv:Body>
    <adr:getAdrrec soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" clover:inPort="0">
      <pPostcode xsi:type="xsd:string">$0.postcode</pPostcode>
      <pHuisnr xsi:type="xsd:decimal">$0.huisnummer</pHuisnr>
    </adr:getAdrrec>
  </soapenv:Body>
</soapenv:Envelope>]]></attr>
</Node>
<Node enabled="enabled" guiHeight="65" guiName="HTTP connector" guiWidth="128" guiX="639" guiY="186" headerProperties="Content-Type=application/soap+xml&#10;" id="HTTP_CONNECTOR0" inputField="XMLString" outputField="XMLString" requestMethod="POST" type="HTTP_CONNECTOR">
<attr name="url"><![CDATA[http://localhost:7779/AdresGegevens/AdresGegevens]]></attr>
</Node>
<Node enabled="enabled" guiHeight="65" guiName="Trash" guiWidth="128" guiX="889" guiY="186" id="TRASH0" type="TRASH"/>
<Node enabled="enabled" guiHeight="87" guiName="XMLExtract" guiWidth="128" guiX="163" guiY="175" id="XML_EXTRACT0" schema="${DATAIN_DIR}/pacos-request-normal.xsd" sourceUri="${DATAIN_DIR}/pacos-request-normal.xml" type="XML_EXTRACT" useNestedNodes="true">
<attr name="mapping"><![CDATA[<Mappings>
	<Mapping element="getAdres" outPort="0"
			xmlFields="postcode;huisnummer"
			cloverFields="postcode;huisnummer"/>
</Mappings>]]></attr>
</Node>
<Edge debugMode="true" fromNode="EXT_XML_WRITER0:0" guiBendpoints="" guiRouter="Manhattan" id="Edge3" inPort="Port 0 (in)" metadata="Metadata1" outPort="Port 0 (out)" toNode="HTTP_CONNECTOR0:0"/>
<Edge debugMode="true" fromNode="HTTP_CONNECTOR0:0" guiBendpoints="" guiRouter="Manhattan" id="Edge4" inPort="Port 0 (in)" metadata="Metadata3" outPort="Port 0 (out)" toNode="TRASH0:0"/>
<Edge debugMode="true" fromNode="XML_EXTRACT0:0" guiBendpoints="" guiRouter="Manhattan" id="Edge0" inPort="Port 0 (in)" metadata="Metadata0" outPort="Port 0 (out)" toNode="EXT_XML_WRITER0:0"/>
</Phase>
</Graph>

Anyone any idea what im missing here..??

Thanks in advance!