In Ubuntu server after an upgrade to apache, the process can copy your 000-default file and leave it with the name This can cause issues with your vhost config and lead to unpredictable results. If you do have strange vhost issues, check in /etc/apache/sites-enabled and make sure that there is no duplication and all the files there are required. In my case it was causing the error:

[warn] NameVirtualHost *:80 has no VirtualHosts