Hi,
I had the same problem and solved it.
The error message is in the apache error.log:
PHP Fatal error: Uncaught Error: Call to undefined function tpl_js() in /var/lib/dokuw
iki/lib/tpl/codowik/main.php:36\nStack trace:\n#0 /usr/share/dokuwiki/inc/actions.php(27): include()\n#1 /usr/share/dokuwiki/doku.php(120): act_dispatch()\n#2 {main}\n thro
wn in /var/lib/dokuwiki/lib/tpl/codowik/main.php on line 36, referer: https://192.168.1.7/doku.php?id=start&do=admin&page=config
Solution:
Comment out the 'mail.php' line 36 and the page is loaded.
Replace this line:
<?php echo tpl_js('layout.js'); ?>
For this:
<--?php echo tpl_js('layout.js'); ?-->
I don't tested in fully the template, but I hope it helps you too.