Thanks! Figured it out, I checked the server logs, and these appeared in red:
[Thu Apr 17 13:52:00 2014] [error] [client xx.xx.xx.xx] SecurityException in Application.cpp:530: Handler not found in configuration
[Thu Apr 17 13:52:00 2014] [error] [client xx.xx.xx.xx] Caused by KeyNotFoundException in Configuration.cpp:275: Handler "application/x-httpd-php53" not found
Then I checked the hosting settings, and it was set to PHP 5.2, while I needed to be on 5.4+. I changed it to 5.4 then changed the .htaccess in the AddOn domain to ONLY (specifically had to delete other PHP handler) have:
AddHandler application/x-httpd-php54 .php