ช่วยหน่อยค่ะ ติด error insert ข้อมูลซ้ำเรื่องเวลาค่ะ (asp.net)

protected void Button1_Click(object sender, EventArgs e)
        { 
string sql1 = "SELECT COUNT(*) FROM dataschedule1 WHERE timein between = '" + DropDownList2.SelectedValue + "' and('" + DropDownList3.SelectedValue + "') or timeout between = '" + DropDownList3.SelectedValue + "' and('" + DropDownList2.SelectedValue + "')" ;
            
            SqlConnection conn = new SqlConnection(conStr);
            conn.Open();
            SqlCommand cm = new SqlCommand(sql1, conn);
            int intNumRows;
            intNumRows = Convert.ToInt32(cm.ExecuteScalar());  // ติด error ตรงนี้อ่ะค่ะ

if(intNumRows > 0)
{

    Label7.Visible = true;
    Button1.Visible = false;
}
            else{
                SqlConnection con = new SqlConnection(conStr);
                con.Open();
                string sql = "INSERT INTO  dataschedule1(date,timein,timeout,room,subject,sec,teacher,semester) VALUES (" + "@date,@timein,@timeout,@room,@subject,@sec,@teacher,@semester)";
                SqlCommand cmd = new SqlCommand(sql, con);

                cmd = new SqlCommand(sql, con);
                cmd.Parameters.AddWithValue("date", DropDownList1.SelectedValue);
                cmd.Parameters.AddWithValue("timein", DropDownList2.SelectedValue);
                cmd.Parameters.AddWithValue("timeout", DropDownList3.SelectedValue);
                cmd.Parameters.AddWithValue("room", TextBox3.Text);
                cmd.Parameters.AddWithValue("subject", TextBox7.Text);
                cmd.Parameters.AddWithValue("sec", TextBox4.Text);
                cmd.Parameters.AddWithValue("teacher", TextBox5.Text);
                cmd.Parameters.AddWithValue("semester", TextBox6.Text);
                cmd.ExecuteNonQuery();
                con.Close();


                Label6.Visible = true;
        }
        }