I have versions 1.6.1. The thing is so strange that I can't add pdf files, but not all. Some are added and others are not with the message "An error occurred, file attachment failed" On version 1.5.3 I had the same problem. I thought if I upgraded to a higher version the problem would go away. Unfortunately, that didn't happen. Anyone had the same and can help. The server it is installed on is synology.
PK