I had installed the Nagios3 form package. Installation was fine. I was getting the error message as shown in Screen shot
Even making changes for ACL’s in Apache conf result noting.
Google is always our friend.The link shown below explained about the bug.
I have changed file as shown
Added the index.html in /etc/apache2/conf.d/nagios3.conf. So the line should be
DirectoryIndex index.php index.html