Try

            Dim client As WebClient = New WebClient()

            '  client.Credentials = CredentialCache.DefaultCredentials

            client.Credentials = New System.Net.NetworkCredential("id", "pass")

            Dim request As WebRequest = WebRequest.Create("http://url/folder/")

            request.Credentials = CredentialCache.DefaultCredentials

            request.Timeout = 1200

            request.Method = "HEAD"

            Dim response As HttpWebResponse = CType(request.GetResponse(), HttpWebResponse)

            If String.Compare(response.StatusDescription, "OK", True) = 0 Then

                MsgBox("ok")

            End If

        Catch

            MsgBox("err")

        End Try