I executed installation via repo & apt-get installation method. This error comes when trying to set up Apache and then breaks because it can't find airtime-vhost, however I'm looking at it in sites-available. I also attempted to symlink to sites-enabled to no avail.
I have also removed the airtime directories as well as apache2 directories and attempted reinstall to no avail.
But meanwhile, if you follow this instruction to install PHP5.4, it will install PHP5.5 instead and this requires apache2.4, which could envoke problems with apache...