Problems with node permissions drupal

From drupal.org :
If the site is experiencing problems with permissions to content, you may have to rebuild the permissions cache. Possible causes for permission problems are disabling modules or configuration changes to permissions. Rebuilding will remove all privileges to posts, and replace them with permissions based on the current modules and settings.

Rebuilding may take some time if there is a lot of content or complex permission settings. After rebuilding has completed posts will automatically use the new permissions.

You can find the rebuild button at: Administer » Content management » Post settings

Cant find the button?
If your node_access table has only one row in it or if you don't have an access control module enabled, it won't show up. It would be on the admin » content » post settings page otherwise.

If you are really intent on rebuilding them, you can create a php page that calls node_access_rebuild().

In drupal 6 you might clear your cache. I experienced this problem while installing og. Clear your cache at admin/settings/performance