You are trying to access a page or resource which s absolutely forbidden for some reason. Following are the possible reasons or remedies to rectify it...
1) 403 Forbidden error can happen because of incorrect ownership or permissions. Remember Rule of thumb for permissions:
Static Content: 644
Dynamic Content: 700
2) Missing Index Page
Home page of any site should be index.php or index.html, To resolve this error, upload an index page to your httpdocs directory.
If you already have a home page then rename your home page to index.html or index.php or Set up a redirect on the index page to your real home page.
3) Empty httpdocs directory or htdocs in apache2
Make sure that your website content has been uploaded to the correct directory on your server. Many a times we forget to replace example.com with our own domain name.