Uploaded images are broken

I just did a fresh install of WordPress Multisite and the main site is working fine. I created some sites but when I upload an image, it shows the image as broken. The files are uploaded correctly to /wp-content/uploads/sites/13/2013/08/

Here’s my .htaccess (WPSuperCache portion not showing):

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) wordpress/$1 [L]
RewriteRule ^(.*\.php)$ wordpress/$1 [L]
RewriteRule . index.php [L]
# END WordPress