Sending XML via ASP page - msxml3.dll error 'c00ce56d'

I get the following error when trying to send XML to a remote server

msxml3.dll error 'c00ce56d'

System error: -1072896659.

Here is the function that is causing the error

private function xmlsend(url, docSubmit)
Set poster = Server.CreateObject("MSXML2.ServerXMLHTTP")
poster.open "POST", url, false
poster.setRequestHeader "CONTENT_TYPE", "text/xml"
poster.send docSubmit
Set NewDoc = server.createobject("Microsoft.XMLDOM")
newDoc.ValidateOnParse= True
newDoc.LoadXML(poster.responseTEXT)
Set XMLSend = NewDoc
Set poster = Nothing
end function

I bulid a string line by line containing the XML info then I use the following code

Set SendDoc = server.createobject("Microsoft.XMLDOM")
SendDoc.ValidateOnParse= True
SendDoc.LoadXML(xmlString)

'Set the URL of the receiver
sURL = "https://epayhipvar.paymentech.net" 

'Call the XML Send function (defined below)
set NewDoc = xmlSend (sURL, SendDoc)'xmlString)

This obviously calls the function above.

This is my first attempt at sending XML and I am not sure where to begin