Store works fine but admin page give HTTP ERROR 500

Also, not sure if the issue has been resolved, but if you still have a copy of your new admin directory files that was used to populate your current site, then you could always generate a new admin directory and populate it with those same files. Then be sure that any changes needed to the YOUR_SECRET_ADMIN/includes/configure.php file were correct. Basically "abandon" the old path and get the files/directory straight. Once that's done then remove the old directory.