Sending MailMessage Using ASP.Net 4.0

Hello,
I have updated some code that sends an email message from an ASP.Net 2.0 application to an ASP.Net 4.0 application.  An error is now thrown when trying to send that simply says "failure sending mail" and the stack trace points to System.Net.Mail.SMTPClient.Send.  Does anyone know if MailMessage or SMTPClient has changed with 4.0?  What needs to change?

Here is my code:

sToAddress = "user@test.com;user2@test.com"
sCCAddress = "user@abc.com;user2@abc.com"
sBCCAddress = "user@xyz.com;user2@xyz.com"
sFromAddress = "someone@somewhere.com"
sSubject = "this is the subject"
sBody = "This is the Body"

                If sToAddress <> "" Then
                    sToAddress = sToAddress.Replace(";", ",").Trim()
                End If
                If sCCAddress <> "" Then
                    sCCAddress = sCCAddress.Replace(";", ",").Trim()
                End If
                If sBCCAddress <> "" Then
                    sBCCAddress = sBCCAddress.Replace(";", ",").Trim()
                End If

                'Send the email message
                    Dim MailMsg As New MailMessage
                    MailMsg.From = New MailAddress(sFromAddress)
                    If sToAddress.IndexOf(",") > 0 Then
                        arToAddress = sToAddress.Split(",")
                        For i = 0 To UBound(arToAddress)
                            MailMsg.To.Add(arToAddress(i).Trim())
                        Next
                    Else
                        MailMsg.To.Add(sToAddress)
                    End If
                    If sCCAddress <> "" Then
                        If sCCAddress.IndexOf(",") > 0 Then
                            arCCAddress = sCCAddress.Split(",")
                            For i = 0 To UBound(arCCAddress)
                                MailMsg.CC.Add(arCCAddress(i).Trim())
                            Next
                        Else
                            MailMsg.CC.Add(sCCAddress)
                        End If
                    End If
                    If sBCCAddress <> "" Then
                        If sBCCAddress.IndexOf(",") > 0 Then
                            arBCCAddress = sBCCAddress.Split(",")
                            For i = 0 To UBound(arBCCAddress)
                                MailMsg.Bcc.Add(arBCCAddress(i).Trim())
                            Next
                        Else
                            MailMsg.Bcc.Add(sBCCAddress)
                        End If
                    End If

                    MailMsg.Subject = sSubject
                    MailMsg.Body = sBody

                    Dim SmtpMail As New SmtpClient
                    Dim SMTPUserInfo As New System.Net.NetworkCredential("user@emailhost.com", "smptpassword")
                    SmtpMail.Host = "SmtpServer"
                    SmtpMail.Port = "25"
                    SmtpMail.UseDefaultCredentials = False
                    SmtpMail.Credentials = SMTPUserInfo

                    SmtpMail.Send(MailMsg)

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