Cant open form in edit mode

if i create an applicatio link from grid to a form (in edit/update mode), form does not find that record (i echoed the select in on app in it in the form, its coming perfect)
why i cant load a form in edit mode?
using
version 9.12.028 (12)

ok i got it, primary key also has to be mapped while creating application link from grid to form
hope it benefits all