Loading custom user account page failing

I’m helping a friend get his WP up to the latest version (3.1) and things are working except: custom user account and custom submit page won’t load. These pages have their own .PHP files, too. The link to the pages have the parameters ‘?mp=user_account’ and ‘?mp=user_submit’ respectively. Clicking the link takes you straight back to the main page, however. I am completely stumped. I have PHP and JS programming experience, so am not timid in regards to getting into the code, but I’m lost. Can anyone help? Thanks in advance!