Try this and let us know if it works:
Const SXH_SERVER_CERT_IGNORE_ALL_SERVER_ERRORS = 13056
Dim xmlHttp As New ServerXMLHTTP50
xmlHttp.Open "POST", strServer, False
xmlHttp.setRequestHeader "Content-Type", "text/xml"
xmlHttp.setOption 2, SXH_SERVER_CERT_IGNORE_ALL_SERVER_ERRORS
xmlHttp.send...