I'm trying to 'roll my own' SOAP messages in order to 'opt-out' contacts from one of our ASP pages on our website.  I can login alright, but then when I try sending the update, I get back "The AXIS engine could not find a target service to invoke! targetService is u/2.5".  I am sending this message the url that is returned with the login (https://na1-api.salesforce.com/services/Soap/u/2.5).

Any ideas what the issue is?  Is it a problem with the namespace?

Sorry if the following does not appear formatted.

The Request (note: I modified the session string):

<SOAP-ENV:Envelope xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <SOAP-ENV:Header>
  <ns1:SessionHeader SOAP-ENV:mustUnderstand="0" xmlns:ns1="SoapService">
   <ns2:sessionId xmlns:ns2="urn:enterprise.soap.sforce.com">WrLj2MGF5bFg1Nm5b</ns2:sessionId>
  </ns1:SessionHeader>
 </SOAP-ENV:Header>
 <SOAP-ENV:Body>
  <update xmlns:ns="urn:enterprise.soap.sforce.com">
   <sObjects xsi:type="ns3:Contact" xmlns:ns3="urn:sobject.enterprise.soap.sforce.com">
    <ns3:Id>00330000002Uxn2</ns3:Id>
    <ns3:HasOptedOutOfEmail>true</ns3:HasOptedOutOfEmail>
   </sObjects>
  </update>
 </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

The Response:

<soapenv:Envelope 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:Body>
  <soapenv:Fault>
   <faultcode xmlns:ns1="http://xml.apache.org/axis/">ns1:Server.NoService</faultcode>
   <faultstring>The AXIS engine could not find a target service to invoke! targetService is u/2.5</faultstring>
   <detail/>
  </soapenv:Fault>
 </soapenv:Body>
</soapenv:Envelope>