Default image not working - Access Denied (even for admin)

I have an image field in a node type. If left blank I set a default image that I uploaded to be displayed. However Drupal doesn't want to display it. I even checked, the image is there in the correct folder. When I go to edit the image field I see that the image is apparently at: http://local.mywebsite.com/system/files/default_images/no_poster.png, but going to that address gives me an access denied (and I'm the admin!). I'm using the private file system under Drupal 7.12. I already cleared cashes multiple times, so I don't know what to think of next.

Your help would be appreciated.
Thanks.