Can't edit entries for just one form

I have two active forms on http://www.boarddiversity.com.au: contact and job vacancies.

Entries for the contact form can be edited via the dashboard, but trying to edit any entries from the jobs form results in a 404 error.

I have upgraded the theme (Nova by Elegant Themes), updated all plugins (s2member, Gravity Forms Directory, Widget Context, Shortcode Redirect to Shortcode, Video Embed & Thumbnail generator). I have also deactivated all plugins except Gravity Forms and switched to the Twenty Twelve theme to see if that helps, but I'm still getting the same problem.

Can you help?

As per my original post I did switch to the default theme and test the issue with only Gravity Forms enabled, but just to double check I switched to Twenty Twelve (don't even have Twenty Ten installed), deactivated all plugins and reenabled just Gravity Forms. The problem still occurs.

It seems unlikely to be a server misconfig because editing entries from a different form works, it's just from this other form.

I am using the latest versions of everything.

I'm going to try exporting the entries and duplicating the form to see if I can get it working again... Any other suggestions welcome.