umm this is strange... Class PDO is a PHP predefined object that should be available to everyone, its weird how the script is trying to load a class PDO with autoloader and fails. Please do consult your host and see what they have to say.
And btw, does this happen to you all the time or just today?
Edit: See the thread below for reference. It may be due to the fact that your host is running some kind of maintenance process on the server, or someone accidentally changed the settings of php.ini.
http://x10hosting.com/forums/free-ho...not-found.html