I have this problem also, but I think this due to the updates that i've made. My server works fine, or not because i've made the update for apache2 and now ISPCOnfig3 control panel shows me that the web-server is offline... but my site's are up.
Code:
* Restarting web server apache2 Warning: DocumentRoot [/var/www/ispconfig/] does not exist
Warning: DocumentRoot [/usr/local/ispconfig/interface/web/] does not exist
Warning: DocumentRoot [/var/www/ispconfig/] does not exist
Warning: DocumentRoot [/usr/local/ispconfig/interface/web/] does not exist
(13)Permission denied: make_sock: could not bind to address 0.0.0.0:80
no listening sockets available, shutting down
Unable to open logs
[fail]
Now i have to see what is wrong, but if you people can give a little help... please do so.