unserialize($obj) this line may cause error in previous version of php < 5.4
because they do not support array dereference you can check http://php.net/manual/en/language.types.array.php
What you can do is, change the code to support previous version or update the version of php in hosting server or local server where you hosted your application.
Change of unserialize code to accept previous version
$tmp = unserialize($obj);
$element = $tmp;