Message box run behind the browser
<p>I have a pop out message box, what I want is the message box always pop out in front of the browser when it is clicked, but the problem is it sometimes pop out behind the browser.
Anything I can do to make sure the message box is always pop out in front the browser?
Thanks.</p>

<pre><code>protected void Button1_Click(object sender, EventArgs e)
{
    string appointmentdate = Convert.ToString(DropDownListDay.Text + "-" + DropDownListMonth.Text + "-" + DropDownListYear.Text);
    string appointmenttime = Convert.ToString(DropDownListTime.Text);


    using (SqlConnection con = new SqlConnection("Data Source=USER-PC;Initial Catalog=webservice_database;Integrated Security=True"))
    {
        con.Open();
        SqlCommand data = new SqlCommand("Select COUNT(*) from customer_registration where adate='" + appointmentdate + "'AND atime='" + appointmenttime + "'", con);
        Int32 count = (Int32)data.ExecuteScalar();
        if (count == 0)
        {
            SqlConnection con1 = new SqlConnection("Data Source=USER-PC;Initial Catalog=webservice_database;Integrated Security=True");
            SqlCommand cmd = new SqlCommand("UPDATE customer_registration SET servicetype = @servicetype, comment = @comment, adate = @adate, atime = @atime where username='" + Session["username"] + "'", con1);
            con1.Open();

            cmd.Parameters.AddWithValue("@servicetype", DropDownListServicetype.Text);
            cmd.Parameters.AddWithValue("@comment", TextBoxComment.Text);
            cmd.Parameters.AddWithValue("@adate", DropDownListDay.Text + "-" + DropDownListMonth.Text + "-" + DropDownListYear.Text);
            cmd.Parameters.AddWithValue("@atime", DropDownListTime.Text);
            cmd.ExecuteNonQuery();

            con1.Close();
            Response.Redirect("MakeAppointmentSuccess.aspx");
        }
        else
        {
            MessageBox.Show("This appointment is not available. Please choose other date &amp; time.");
            con.Close();
        }
    }
}
</code></pre>
