HttpWebRequest Problems encountered

Dim postData As String = "author=" & txtUser.Text & "&email=" & txtEmail.Text & "&url=" & txtWebsite.Text & "&comment=" & txtMessage.Text & "&submit"
'If i try this as Post Data, it wont let me post to my wordpress site. it returns nothing.
'If it try this 
' "author=" & txtUser.Text & "&email=" & txtEmail.Text & "&url=" & txtWebsite.Text & "&comment=" & txtMessage.Text & "&submit=&comment_post_ID=" & tempInt '- it returns me 'as code 500, Internal Server error.

    Dim tempcookies As New CookieContainer
    Dim encoding As New UTF8Encoding
    Dim byteData As Byte() = encoding.GetBytes(postData)
    Dim postreq As HttpWebRequest = DirectCast(HttpWebRequest.Create("http://myurl.com/wp-comments-post.php"), HttpWebRequest)
    postreq.Method = "POST"
    postreq.KeepAlive = True