Data in not displayed on checkbox in c#.net sqlserver : i am tring diplay the values from database. textbox values displayed successfully but checkbox values is not diplayed and it shown the error. i attached the error on screenshot image below

 [enter image description here][1]

    sql = "select * from repair where repairid = '" + repairid + "'";
                    SqlCommand cmd = new SqlCommand(sql, con);
                    SqlDataReader dread;
                    con.Open();
                    dread = cmd.ExecuteReader();
        
                    while (dread.Read())
        {
        checkBox7.CheckState = dread[6].ToString();
        }
    
    
      [1]: https://i.stack.imgur.com/fIf3h.jpg


  [1]: https://i.stack.imgur.com/97BXW.jpg