Smtp Mail - errore strano

Dim mail As New MailMessage
        Dim smtp As New SmtpClient("mail.multixxxxx.com")
        Try
            mail.From = New MailAddress(TextBox2.Text)
        Catch ex As Exception
            MsgBox(ex.Message)
            Exit Sub
        End Try
        mail.To.Add("info@multixxxxxx.com")
        mail.Subject = (TextBox3.Text)
        mail.Body = "Richiesta informazioni da " & TextBox1.Text + vbCrLf + vbCrLf + TextBox4.Text
        Dim allegato As Attachment
        Directory.SetCurrentDirectory(Server.MapPath("~/Contatti/Allegati/"))
        Dim percorso As String
        For i = 0 To ListBox1.Items.Count - 1
            percorso = CurDir() + "/" + ListBox1.Items(i).Value
            allegato = New Attachment(percorso)
            mail.Attachments.Add(allegato)
        Next
        smtp.Credentials = New System.Net.NetworkCredential("info@multixxxxx.com", "xxxxxxxx")
        smtp.Send(mail)

    End Sub