阻止PHP 5.5中的require语句

Question

I used to ran my website with PHP 5.3 and everything worked great. After upgrading to 5.5.9-1ubuntu4.7 (what phpversion() says), my facebook login script file gets blocked at the line:

require 'facebook-php-sdk-master/src/facebook.php';

either I write it like that as indicated in the facebook documentation, or like

require('facebook-php-sdk-master/src/facebook.php');

So, I cannot figure out what happens here and I think that it should be a PHP issue. Any clue?

Note. The facebook SDK that I use in the require statement is deprecated but it still runs with my PHP 5.3, but not with PHP 5.5.9-1ubuntu4.7.