error Posting XML with characters in a Mac Address

I am posting an XML string to a server that logs users connecting to my mySQL database.
one of the variables is a Mac Addresseg: fe80::25ea:dfaa:bdd0:32f%11.

Im guessing the issue is the non alphanumeric characters as non utf-8 ?  but im not sure
here is the code Im using maybe someone can help me figure out why my program is crashing because of the IP address.

Imports System
Imports System.IO
Imports System.Net
Imports System.Text
Public Class logVbUser
    Public Shared responseFromVbLogger As String
    Public Shared Sub Main(ByVal customerId As Integer, ByVal userId As Integer, ByVal pcName As String, ByVal macAddress As String)
        Dim xml As String
        xml = "logRequestMode=X&logRequestData="
        xml += "<?xml version='1.0' encoding='UTF-8'?>"
        xml += "<TranxRequest>"
        xml += "<CompanyId>" & customerId & "</CompanyId>"
        xml += "<UserId>" & userId & "</UserId>"
        xml += "<pcName>" & pcName & "</pcName>"
        xml += "<macAddress>" & macAddress & "</xxxName>"
        xml += "</TranxRequest>"

        ' Create a request using a URL that can receive a post. 
        Dim request As WebRequest = WebRequest.Create("http://" & databaseConnection.dbServer & "/includes/vbNetLogger.php")
        ' Set the Method property of the request to POST.
        request.Method = "POST"
        ' Create POST data and convert it to a byte array.
        Dim postData As String = xml
        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()
        ' 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.
        responseFromVbLogger = responseFromServer
        Console.WriteLine(responseFromServer)
        ' Clean up the streams.
        reader.Close()
        dataStream.Close()
        response.Close()
    End Sub
End Class

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