you need to set the action of the form to post to the second page, an add the server validation to the second page as well.
on the second page, go to the bindings panel, click the plus button and select Form Data, click the folder icon and select the first page to add dynamic data bindings for the form from the first page.
then add the server validation server behavior to validation the form, and use the post to capture the form variables into hidden.
The issue is that form post data only exists while the forms action page is processing, once that page finishes processing or the page is redirected, the post is destroyed.