mi da questo errore quando lancio la creazione del file

Warning: fopen(gallery.xml): failed to open stream: Permission denied in /usr/local/psa/home/vhosts/davidefrancese.it/httpdocs/new/buildgallery.php on line 115

Cannot open XML document: gallery.xml

Warning: fclose(): supplied argument is not a valid stream resource in /usr/local/psa/home/vhosts/davidefrancese.it/httpdocs/new/buildgallery.php on line 122