Internal Server Error 500

[Breaking]

I keep getting IIS 500 internal error from the SOAP post
rather than the details of the error.
I have an XMl doc as
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<SessionEnd xmlns="http://tempuri.org/Management/">
<SessionEndRequest
xmlns="http://localhost/Schema/SessionEnd">
<ServiceHeader>
<Identification
xmlns="http://localhost/Schema/ServiceTypes">
<CLID>
<LoId>123</LoId>
<EndId>EndID</EndId>
</CLID>
</Identification>
<SessionId
xmlns="http://localhost/Schema/ServiceTypes">7bca6197-441a-4a34-b166-608744ee95d8</SessionId>
</ServiceHeader>
</SessionEndRequest>
</SessionEnd>
</soap:Body>
</soap:Envelope>
I post it the web service through the Web Request.
Since the XML doc is valid it pass the schema validation in
the web service and i get the desired result.
If i remove one of the element from the above xml doc it
fails on schema validation, in the schema validation I able
to write the reason for the fail in log, but on the client
side it returns IIS 500 Internal error.
I the option show Friendly HTTP error messages turned off
in IE.
Can any one help me with this problem?
Thanks in advance.