The file directory is not writable.
/home/aiena/domains/file.aiena.de/public_html/var-qZqYj0FxjAQDPux/files/

The link directory is not writable.
/home/aiena/domains/file.aiena.de/public_html/var-qZqYj0FxjAQDPux/links/

The async directory is not writable.
/home/aiena/domains/file.aiena.de/public_html/var-qZqYj0FxjAQDPux/async/