This is probably a per-user issue. When you run the program from the command line, are you logged in as the user account for the web server?

The user that Apache runs under is often 'apache', 'httpd', 'nobody', or 'www'. These are limited-rights accounts that do not have the same environment and file rights as most local users. This is to protect your system, because if a security bug is exploited on your web server, you don't want the code to have many rights.

Check to see if the files you're having trouble using are readable by the web server's user account. Try 'ps aux | grep apache', 'ps aux | grep httpd', or 'lsof /var/log/httpd/error_log' or similar to see under which account Apache operates.