APEX

Application has 4 pages (P1, P2, P4, P5), plus Login page. Description is following:
Page P1 and P2 are wizard created Form and Report page type and List of Values has been added on page P1 to select specific record in table report on page P1.
From page P1 to P2 we go with the wizard created button to create a new record or with the created link button (Edit) in table report to edit specific record.
On page P2 there is template submit button "Loc" that executes "Branch to page"
(Branch Point=OnSubmit: After Processing, Conditions: When button pressed = "Loc", target type=Page in This Application, page = P4 with setting a couple items with the values).
When I applied Session State Protection-Arguments Must Have Checksum on all pages we get error:
"No checksum was provided to show processing for a page that requires a
checksum when one or more request, clear cache, or argument values are passed as parameters. "
when form page P4 we return to page P2 with template based button "Exit" with Optional URL Redirect settings: Target="Page in this Application", Page=2, and set 2 items on Page P2 with values.

If I set page P2 from Session State Protection: Arguments Must Have Checksum to Unrestricted and leaving other 3 pages with Arguments Must Have Checksum, it works fine but we do not have protection on page P2. That is a Problem.

Do I need to apply call to page P4 with button " Loc" using method HTMLDB_UTIL.prepare_url to wrap link to call page P4 from page P2 ( and how to do it ) or I am doing some other things wrongly?

Thanks,
Brano