For some additional data-gathering, you can edit the file /includes/application_top.php, finding this line:
Code:
define('DEBUG_AUTOLOAD', false);
and changing that to read
Code:
define('DEBUG_AUTOLOAD', true);
That will cause the auto-load status to be displayed for each item processed. There might be a missing class-file or some other obscure issue and that display will aid in that determination.

Remember to turn that back to false (no quotes) when you're finished.