file maniputation??

Hey all. I have a script that uses that creates/manipulates files, and it works great on my end. Thats no question. There is a small percentage of my users that when they try to run the file it cannot create or modify files. I suspected file ownership may be wrong on files and directories. Just in case Im wrong, what else could be the matter?? Example code. $file = "foo/bar/example.php"; $config = array("x", "y", "z"); if ($fp = fopen($config_file, "wb")) {

        foreach ($config as $line) {
            fwrite($fp, "$line\n");
        }

Example error. Warning: fopen("foo/bar/example.php","wb") - Permission denied in /usr/local/psa/home/vhosts/httpsdocs/install.php on line 3429 Thanks