The problem lies here I guess.......
OleDbCommand cmd = new OleDbCommand("select * from Temp where Book_code='"+textBox2.Text+"'");
Why don't you tell the command on which connection will it run like
OleDbCommand cmd = new OleDbCommand("select * from Temp where Book_code='"+textBox2.Text+"'",con);
Best of luck.....
Hope it helps