Thanks for that Kikkerking.
Simple issue - after seeing that you had a custom admin directory, it was quick to notice that you didn't upload the updated /admin/myplaza.php
I've done it for you. Oh yeah, BTW, I've uploaded a v0.53 /admin/myplaza.php, in which I've added a Quick Add Category. Since I haven't uploaded the language file, the title will be blank. Not to worry about though
I also fixed up your template issue.
Out of interested, did you run the upgrade script? Cause I thought it was meant to rebuild the templates...
I did forget to ask you for an admin account, so I made one myself. If you have no further issues, you can remove/delete/whatever with it