Can't load node_privacy_byrole module

When I extract the node_privacy_byrole.module into "modules" and then go to the administer/modules page, I get this error:

warning: is_dir(): Stat failed for modules/node_privacy_byrole.module (errno=13 - Permission denied) in /var/www/html/includes/file.inc on line 527.

warning: drupal_load(modules/node_privacy_byrole.module): failed to open stream: No such file or directory in /var/www/html/includes/bootstrap.inc on line 342.

warning: drupal_load(): Failed opening 'modules/node_privacy_byrole.module' for inclusion (include_path='.:/usr/share/pear') in /var/www/html/includes/bootstrap.inc on line 342

on the top of the page before the modules listing. The listing DOES show the module but doesn't show the description.

I've noticed this before when I added new modules, and found that by removing the ones I wasn't using it would be fixed. I've moved out 4 modules this time and it still won't load, so I don't know if it's a problem with this module or the admin/modules process (like there's some sort of limit being reached?).

To install the module I did an extract straight from the tar file into the modules directory. Here's the permissions on the file:

-rwxr--r-x 1 drupal drupal 25549 Jun 10 19:15 node_privacy_byrole.module

p.s. I tried it with both the 4.6.0 version and the cvs.

Thanks :-)

Vicki