I removed wall paper from a 'plaster board' wall. (I think it's called
plaster board, It's a thin coat of plaster over a hard rock like board -
not the old wood lathes though) The home was built in the early 70's.

Anyway, I removed the wall paper. The wall below was never painted. I
patched some holes and lightly sanded the entire wall.

I then painted the wall with a Behr Primer and let it set for two days. I
then taped off some squares in the field of the wall to paint some
decorative squares (its a kids room... ask my wife). Well, you can probably
guess where this is going. The tape is pulling the primer off the wall.
Help. What did I do wrong?

It only pulled off in some areas. In the areas that it did peel I can pull
off peices of paint several inches long and wide. Before priming I did wipe
down the wall to get the dust off.

Also, The wall surface is very smooth.

How do I fix this mess. I assume I need to scrape off anything that will
come down but then what? How can I be sure the next primer coat will adhere
properly

thanks