Admin area doesn't work

Sorry for my bad English; but my motherlanguage isn't English

I have integrated this guesbook in my site; and after some modifications it works fine. Only the admin doens't work any more.
If I want to login; I click on 'Onderhoud' (dutch for admin); but there is no output. There's not one letter I see.

I have integrated the guestbook into my site with the standard PHP variable 'include'. The link to go to my admin is so 'index.php?inhoud=gastenboek&gboek=admin'
The problem is (I think) that the refferer page is not good, and that the build-in security gives no output. But am I right; and how can I fix that?

The site: http://htb.ath.cx/index.php?inhoud=gastenboek&gboek=index
Directly to admin: http://htb.ath.cx/gastenboek/admin.php

I hope someone can help me;
Regards

Kijk eens naar Lazarus

Mm, op zich heel interessant, maar hoeveel wordt er nou veranderd?
Kan ik alle templates zo houden? Ik heb er nl. wel wat tijd in gestoken; en ben natuurlijk niet van plan om nog een keer hetzelfde te doen.

Well Lazarus uses the .tpl extension and not .php. This is for security reasons. There are some changes in the Lazarus templates but having seen your site it wouldn't take long to convert Lazarus to your current style.