help please...get this when i try to log in...

Warning: main(includes/application_top.php): failed to open stream: Permission denied in /blah/blah/blah/login.php on line 23

Warning: main(includes/application_top.php): failed to open stream: Permission denied in /blah/blah/blah/login.php on line 23

Fatal error: main(): Failed opening required 'includes/application_top.php' (include_path='.:/usr/local/lib/php:/usr/local/lib/php/PEAR:/usr/local/share/pear') in /blah/blah/blah/login.php on line 23

can't figure out what i did wrong as comparing old and new php found no difference....maybe i set permissions wrong?!*# ....or if you can help i would greatly appreciate it.

thank you in advance from poor clueless me