OpenX and HostGator shared hosting
OpenX does not work on HostGator’s default shared hosting. Every ad you post on your website through OpenX will be viewable, but clicking the ad will lead to a 403 forbidden page.
It has something to do with HostGator Apache’s default configuration on shared hosting. Globally, it is because of some configuration of mod_security, but I don’t know what it is exactly. I found out that you can’t turn off mod_security within the .htaccess. Thanksfully, the tech team will fix you up through the live support within minutes.
The page isn't redirecting properly after a successful upgrade
This happened in firefox, just clear all your browser data (cache, cookies, etc.).