I have the same error
Do you use the docker version ?
In the logs under /volume1/Docker/qBittorrent/config/data/qBittorrent/logs, i got this :
File error alert. Torrent: "Room.104.S04E11.1080p.WEB.H264-CAKES[rarbg]". File: "/volume1/Download/En_cours/Room.104.S04E11.1080p.WEB.H264-CAKES[rarbg]/room.104.s04e11.1080p.web.h264-cakes.mkv.!qB". Reason: Room.104.S04E11.1080p.WEB.H264-CAKES[rarbg] mkdir (/volume1/Download/En_cours/Room.104.S04E11.1080p.WEB.H264-CAKES[rarbg]/room.104.s04e11.1080p.web.h264-cakes.mkv.!qB) error: Permission denied
But, directories from /volume1 are in 777 :
drwxrwxrwx 31 root root 4.0K Sep 23 20:11 volume1/
drwxrwxrwx 4 admin administ 32.0K Oct 1 07:58 Download/
drwxrwxrwx 2 admin administ 4.0K Oct 3 17:07 En_cours/
Do you have any clues ?
PS : ports 6881 (tcp/udp) and 1881 are open on asustor and on my ISP router