The method Zend_Loader::isReadable() uses fopen to check if a file exists and the @-operator to abort its error-messages: public static function isReadable($filename) { if (!$fh = @fopen($filename, 'r', true)) { return false; } return true; } This only aborts the messages from beeing displayed, the error-handler will be triggert anyway. So if you use your own error-handler, everytime a file is beeing checked with this function and not found (and this may happen very often) a php-notice is thrown and beeing logged into your logfile for example or your database. Why not use the 'file_exists()' function of php? // example with include path: static $paths = null; if ($paths == null) { $paths = explode(PATH_SEPARATOR, get_include_path()); } foreach ($paths as $path) { $fullpath = $path.DIRECTORY_SEPARATOR.$filename; if (file_exists($fullpath)) { return true; } } return file_exists($filename);