Pre populate fields with query string?

Hi,
ok i try now your solution with a link back to the form and then pre-populate some fields. But i can't get it to work.

See this post (last reply):

http://www.gravityhelp.com/forums/topic/conditional-logic-add-max-8-times-extra-data-by-selecting-radio-button

What i did:
- in 'edit' form field >> advanced tab >> i select 'Allow field to be populated dynamically' and give a parameter name 'org-naam'

- In the confirmation message i put a link:
'klik hier'

Is this query string good?

But now after you click the link and return to the form, the 'Naam' field is still empty? So the field is not pre populated.

What am i doing wrong?

Thanks.