I am trying to run a query using the API by generating my own SOAP messages. I can login successfully but I get an Invalid Session ID when I run the query. I am using the ServerURL and SessionID generated by the login result in my query call. Below is a packet capture of my login call, response, query call and response. Any ideas?

POST /services/Soap/u/21.0 HTTP/1.1
Connection: Keep-Alive
Content-Type: text/xml
Accept: */*
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; Win32; WinHttp.WinHttpRequest.5)
SOAPAction: ""
Content-Length: 562
Host: test.salesforce.com

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SOAP-ENV:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body>
<mns:login xmlns:mns="urn:partner.soap.sforce.com">
<mns:username xsi:type="xsd:string">user@domain.com.test
</mns:username>
<mns:password xsi:type="xsd:string">PaSsWoRd
</mns:password>
</mns:login>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

------------------------------------------------------------------------------------------------------------
HTTP/1.1 200 OK
Server: 
Content-Type: text/xml; charset=utf-8
Date: Thu, 27 Jan 2011 15:16:51 GMT
Content-Length: 1753
Connection: Keep-Alive

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns="urn:partner.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<loginResponse>
<result>
<metadataServerUrl>https://tapp0-api.salesforce.com/services/Soap/m/21.0/00DT0000000****
</metadataServerUrl>
<passwordExpired>false
</passwordExpired>
<sandbox>true
</sandbox>
<serverUrl>https://tapp0-api.salesforce.com/services/Soap/u/21.0/00DT0000000****
</serverUrl>
<sessionId>00DT0000000****!AR8AQN********CatI6TXoKHzL8EAVFCRGd********yYwhAhbBFj4HehdoQW3********aBn11YgE3Jx********IUGeOft
</sessionId>
<userId>00520000000*******
</userId>
<userInfo>
yada-yada
</userInfo>
</result>
</loginResponse>
</soapenv:Body>
</soapenv:Envelope>

------------------------------------------------------------------------------------------------------------
POST /services/Soap/u/21.0/00DT0000000**** HTTP/1.1
Connection: Keep-Alive
Content-Type: text/xml
Accept: */*
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; Win32; WinHttp.WinHttpRequest.5)
SOAPAction: ""
Content-Length: 759
Host: tapp0-api.salesforce.com

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SOAP-ENV:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Header>
<SessionHeader>
<sessionId>00DT0000000****!AR8AQN********CatI6TXoKHzL8EAVFCRGd********yYwhAhbBFj4HehdoQW3********aBn11YgE3Jx********IUGeOft
</sessionId>
</SessionHeader>
</SOAP-ENV:Header>
<SOAP-ENV:Body>
<mns:query xmlns:mns="urn:partner.soap.sforce.com">
<mns:queryString xsi:type="xsd:string">SELECT Id, Name, BillingStreet FROM Account WHERE Name LIKE 'Test%'
</mns:queryString>
</mns:query>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

------------------------------------------------------------------------------------------------------------
HTTP/1.1 500 Internal Server Error
Server: 
Content-Type: text/xml; charset=utf-8
Date: Thu, 27 Jan 2011 15:18:00 GMT
Content-Length: 700
Connection: Keep-Alive

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:sf="urn:fault.partner.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<soapenv:Fault>
<faultcode>sf:INVALID_SESSION_ID
</faultcode>
<faultstring>INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session
</faultstring>
<detail>
<sf:UnexpectedErrorFault xsi:type="sf:UnexpectedErrorFault">
<sf:exceptionCode>INVALID_SESSION_ID
</sf:exceptionCode>
<sf:exceptionMessage>Invalid Session ID found in SessionHeader: Illegal Session
</sf:exceptionMessage>
</sf:UnexpectedErrorFault>
</detail>
</soapenv:Fault>
</soapenv:Body>
</soapenv:Envelope>