Thanks for the answer.
But no, I'm sorry, there's nothing wrong with my .htaccess file (I think). Here's my .htaccess file:
####CUSTOM_HEADER####
#NL: Place your custom rules here
####CUSTOM_TAILER####
####ERROR_HEADER####
ErrorDocument 400 /404.php
ErrorDocument 401 /404.php
ErrorDocument 403 /404.php
ErrorDocument 404 /404.php
ErrorDocument 500 /404.php
####ERROR_TAILER####
####SUBDOMAINS_HEADER####
#RewriteEngine on
#RULE:www.mozes,drek.nl,/Mozes
#RULE:mozes,drek.nl,/Mozes
#RewriteCond %{HTTP_HOST} ^
www.mozes.drek.nl$#RewriteCond %{REQUEST_URI} !^/Mozes/
#RewriteRule (.*) /Mozes/$1 [last]
#RewriteCond %{HTTP_HOST} ^mozes.drek.nl$
#RewriteCond %{REQUEST_URI} !^/Mozes/
#RewriteRule (.*) /Mozes/$1 [last]
####SUBDOMAINS_TAILER####
####ACCESS_HEADER####
####ACCESS_TAILER####