cannot implicitly convert type 'system.web.ui.control' to 'system.web.ui.webcontrols.checkbox

using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using System.Drawing;SqlConnection con = new SqlConnection("Data Source=xxxxxxxxxxx ;Initial Catalog=xxxxxxx;Integrated Security=True");
            con.Open();
            SqlCommand cmd = new SqlCommand("select ticketno from order_master where moviename= '" + drpselectmovie.SelectedValue + " 'and moviedate='" + drpselectdate.SelectedValue + "'and show='" + drpselectshow.SelectedValue + "'", con);
            DataTable dt9 = new DataTable();
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            sda.Fill(dt9);
            con.Close();


    int i = 0;

    for (i = 0; i <= dt9.Rows.Count - 1; i++)
    {
        CheckBox ch = new CheckBox();

        ch = Page.FindControl(dt9.Rows[i].ItemArray[0].ToString()); <--- ERROR
        ch.Checked = true;
        ch.Enabled = false;
        ch.BackColor = System.Drawing.Color.Chocolate;
    }

i want to check seat avalability of my system, so user can check selecting show time, so user selected show time system check for available seat from database and disbale checkBox that are booked by other users

so my problem is i'm getting Error on "ch = Page.FindControl(dt9.Rows[i].ItemArray[0].ToString());"

What i'm doing wrong here

Error message: cannot implicitly convert type 'system.web.ui.control' to 'system.web.ui.webcontrols.checkbox'