Apache: Add another site (phpBB3) besides owncloud

Steps to reproduce
1. Install OwnCloud, configure SSL
2. Add phpBB3 to /var/www/phpBB3
3. Add Alias to owncloud.config

Expected behaviour

phpBB3 available on localhost/phpBB3
Actual behaviour

owncloud error page shown
Server configuration
Operating system: Linux Mint 17.2
Web server: Apache2
Database: MySQL
PHP version: 5.5 (not sure atm)
ownCloud version (see ownCloud admin page): 9.1.0 (stable)
Updated from an older ownCloud or fresh install: updated twice
ownCloud log (data/owncloud.log, see https://central.owncloud.org/t/how-to-find-webserver-or-oc-logfile-enable-php-logfile/808):

Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):

Integrity status for oC9+

No errors have been found.

Hi,

moving to the miscellaneous category as this is a webserver configuration issue rather then an ownCloud issue.

If no one in here can help in the next time with this configuration problem you might want to get in touch with a community like http://www.apachelounge.com/

Thanks for the quick reply