เขียน App ด้วย VB.NET เรียกใช้งาน WebService แล้ว Error HTTP/1.1 500 Internal Server Error

Dim request As WebRequest = WebRequest.Create("http://192.168.0.33/SMS_REQ/SevInfo.asmx")        
request.Method = "POST"

Dim postData As String = msg '"This is a test that posts this string to a Web server."
Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData)
       
 ' Set the ContentType property of the WebRequest.
 request.ContentType = "application/x-www-form-urlencoded"
        
' Set the ContentLength property of the WebRequest.
 request.ContentLength = byteArray.Length
        
' Get the request stream.
Dim dataStream As Stream = request.GetRequestStream()
' Write the data to the request stream.
dataStream.Write(byteArray, 0, byteArray.Length)
' Close the Stream object.
dataStream.Close()

' Get the response.
Dim response As WebResponse = request.GetResponse()   '<----- Error ตรงนี้ ว่า 500 Internal Server Error
' Display the status.
Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)
' Get the stream containing content returned by the server.
dataStream = response.GetResponseStream()

' Open the stream using a StreamReader for easy access.
Dim reader As New StreamReader(dataStream)
' Read the content.

Dim responseFromServer As String = reader.ReadToEnd()
' Display the content.
Console.WriteLine(responseFromServer)
' Clean up the streams.
reader.Close()
dataStream.Close()
response.Close()