"Phalcon Exception: Views directory must be a string or an array", but it is a string...(?)

If an answer (even yours) has been accepted, please click the "Accept Answer" button. That will update the post title and let others know the problem has been solved.

Using global is generally frowned upon, because doing so provides no insight as to where that variable is defined. If that variable is defined in the same file and context as the code you posted above, you can use the use directive to import variables from the scope. For example:

$APP_PATH_VIEWS = APP_PATH . SEPARATOR.'views';// removed the leading "", as it's unnecessary.

$di = new Phalcon\DI\FactoryDefault();

$di->set('view', function() use($APP_PATH_VIEWS) {
        $view = new \Phalcon\Mvc\View();
        $view->setViewsDir($APP_PATH_VIEWS);
        return $view;
});