Because i dont have the time to make a new docu entry 
 
Rootkit log prints: 
Code:
Warning: is_readable() [function.is-readable]: open_basedir restriction in effect. File(/var/log/rkhunter.log) is not within the allowed path(s): (/var/run/:/var/www/ispcp/gui/:/etc/ispcp/:/var/run/ispcp.lock:/proc/:/bin/df:/bin/mount:/var/log/rkhunter.log:/var/log/chkrootkit.log:/usr/share/php/) in /var/www/ispcp/gui/admin/rootkit_log.php on line 60
 
because the cron entry is not set propperly:
edit /etc/cron.daily/rkhunter
set: 
then it should work as expected