Buildkit - amp test fails - incorrect response received
The problem was PHP files weren't being processed. I reinstalled PHP module using the following commands and it worked.

sudo /etc/init.d/apache2 stop
sudo apt-get remove --purge apache2 php5
sudo apt-get remove --purge libapache2-mod-php5
sudo apt-get install php5 apache2 libapache2-mod-php5
sudo /etc/init.d/apache2 start
sudo a2enmod php5
sudo /etc/init.d/apache2 force-reload