Hi,
>>

objUnform = CREATEOBJECT("MSXML2.DOMDocument.4.0")
objUnform.Async = .f.
** (strxml is path to the XML file recorded on my local hard disk)
objUnform.Load(strXml)
objHTTP=CREATEOBJECT("MSXML2.XMLHTTP.4.0") 
** The destination is a secure site so mstrURL contains "https etc + user and password"
objHTTP.open("POST", mstrURL,.f., mstrUsername, mstrPassword)
objHTTP.setRequestHeader("Content-Type", "text/xml")
objHTTP.Send(ObjUnform.Xml)

Just a couple of suggestions:
(a) Check that the .load is successful. In fact, assuming the XML is valid, since you have the body in an XML file already then you could just use .Send(FileToStr(strXML)).
(b) Redirect the send to the MSSOAP trace to see what's actually being sent.

HTH,Regards,
Viv