After a Drupal 6 to 7 update we are unable to use private image download, symptom is we cannot access private files via system/files, while public files can be loaded.
Trying to download private file results in a 404 -- Not found error, sent from the web-server directly, not drupal. After some changes to the configuration this results instead in a Drupal Error page. The server log says
File does not exist: /home/licebase/drupal/system/files/genefinding_diagram_1_2.png, referer: https://myhost/node/761470/edit?render=overlay
The system file exists and has the correct permissions.
Centos 6 on virtualization host, PHP 5.3.3, Postgres 8.4 on dedicated DB server, Apache 2.2.15 (centos) + a lot of active modules + fields+cck