Buongiorno a tutti,
ho risolto il problema precedente, ora si presenta quest'altro avviso:

xml:lang attribute value is missing

questo è il codice VB.NEt della chiamata al Webservice SOAP:

Dim retmsg As String = ""
Try
Dim URL3 As String = "https://localhost:8443/ws/dpInviaEsitoPagamento/dpInviaEsitoPagamento.php?WSDL"
Dim address3 As New EndpointAddress(URL3)
Dim binding3 = New WSHttpBinding(SecurityMode.Transport, False)
binding3.Security.Transport.ClientCredentialType = HttpClientCredentialType.Basic
binding3.Security.Message.ClientCredentialType = BasicHttpMessageCredentialType.UserName
binding3.TextEncoding = System.Text.Encoding.UTF8
Dim service3 As New ServiceReference2.WebService1SoapClient(binding3, address3)
service3.ClientCredentials.UserName.UserName = username
service3.ClientCredentials.UserName.Password = password
Dim vmsg = binding3.MessageVersion
Dim retxml2 = service3.dpInviaEsitoPagamento(xmlstr4)
Catch ex As Exception
retmsg = ex.InnerException.Message
End Try

qualche idea?
Grazie