Can't delete card

[Dominique]

When I try to delete a card via a bg script, I am given an Error message

the handler:

on deletekey
  answer "Supprimer cette carte ?" with "Annuler" or "Supprimer"
  if it is "supprimer" then delete this card
end deletekey

the error message:

Object: stack locked, or object's script is executing
Chunk: can't delete object

BUT if I click on a button with a one-line script (delete this card)
that works!
Moreover, if I write a script which sends mouseup to the btn, it doesn't
work again (error message)!

Is there a rationale behind this?

-- 
Regards,
(-8 Dominique