SevenCubed - 2:22 am on Feb 6, 2013 (gmt 0)
What is your hosting environment? Such as: Linux / Apache / MySQL / PHP? Shared, VPS, Dedicated? And are you running PHP scripts as an Apache module, CGI, or fastCGI?
I had a major problem few weeks ago due to fastCGI when I moved from one hosting environment to a new one. Took me all day to find a solution which was nothing like previous syntax:
AddHandler php-script .html
It can be added to .htaccess -- may not work for you but worth a try.