protected void TextBox2_TextChanged(object sender, EventArgs e)
{
DateTime date1 = Convert.ToDateTime(TextBox1.Text);
DateTime date2 = Convert.ToDateTime(TextBox2.Text);
int result = DateTime.Compare(date1, date2);
if (result > 0)
{
Response.Write("<script type='text/javascript'>");
Response.Write("alert('not valid');");
Response.Write("</script>");
}
}