Can’t edit posts with custom fields

Hi, I uppdated my blog to 2.6 and started adding some custom fields to some posts. Now when I try to edit one of this posts I don’t get any forms at all. Only the menu bar of the admin site gets loaded after klicking the edit-link: look here. Posts with no custom fields can be edited without any problems. And after removeing the fields from the database in phpmyAdmin it works aswell.

I already deleted alle WP files and uploaded them again, deactivated all plug-ins and changed the theme (although it’s a problem of the admin interface), but with no effect.

I hope you can help me out.