I get the following error error:can't pack .notebook.tAB_1.button inside .notebook.tAB_2 Please let me know as to what mistake I'm doing

Look at it this way :) its a path

error:can't pack 
          .notebook.tAB_1.button
inside
          .notebook.tAB_2
[download]

its a path

          .notebook.tAB_1.button
          .notebook.tAB_2
[download]

its a parent child relationship

          .grandpa.daddy.baby
          .grandpa.uncle
[download]