ServerHTTP, SSL + Client Certificates?

I have to set up a SSL connection from my client application(vb6.0) sending XML request to some business partner. I got some certificates(nos 4) from this partner & installed it on the computer (by simply double clicking it) where the program runs on.
Previously it was working fine, i was getting the responce. but now got the error : "The server returnned an invalid or unrecognized responce " error.

Can anybody help me out, possibly with a step by step description on what to
do?
Following is the code i m using
'
Dim objDom As New MSXML2.DOMDocument
Dim objXmlHttp As New MSXML2.ServerXMLHTTP40
objDom.async = False
objDom.LoadXml strXML
objXmlHttp.open "POST", strURL, False
objXmlHttp.setRequestHeader "Content-Type", "text/xml; charset=utf-8"
objXmlHttp.setRequestHeader "SOAPAction", strSoapAction
objXmlHttp.setOption 3, "CURRENT_USER\My\tibgwp1.emiratesbank.com"
objXmlHttp.send objDom.xml 'here i got error :(
Set objDom = objXmlHttp.responseXML
'---