Topic: failed to open stream and supplied argument errors

I had no problem the last time I updated my pictures. Can someone help me out please? All permissions are set to 755, is that correct?

Warning: fopen(gallery.xml) [function.fopen]: failed to open stream: Permission denied in /public_html/Stone/buildgallery.php on line 115

Cannot open XML document: gallery.xml

Warning: fclose(): supplied argument is not a valid stream resource in /public_html/Stone/buildgallery.php on line 122