Hi Nick:

First to pack a table , it must be open in EXCLUSIVE mode.
Second , to get exclusive it must be "free" from other users ...
so you can try to help on LOCK() or FLOCK() or..
xONERROR = On("ERROR")
ON ERROR do MyDBFerror
use Mytable
ON ERROR &xONERROR

PROC myDBFERROR
the user is using the table