changed:
		return str_replace('[[client_download_page]]',client_download_files(),$content);

to:


		$content = str_replace('[[client_download_page]]',client_download_files(),$content);
		var_dump($content);
		return $content;


input:
	<h1>Area riservata</h1>	[[client_download_page]]

var_dump outputs:

	string(25) "<h1>Area riservata</h1>"