As a last resort you could try deleting all your Tiki files, and uploading 5.2 from scratch. Of course, make sure you back up all your important files like images/logos/file gallery files. As long as you don't touch your database you should be okay. Then run the installer and hopefully it should figure out where you database is at and update accordingly.
Like I said, this is probably a last resort so you might want to wait for some other responses first.