Hello,
I added a user, group "users", mounted a volume and wanted to allocate a space on this volume to this user (under access control -> shared folders).
It returns the error message: "Failed to set file group to 'users' for '/srv/dev-disk-by-label-USB1/John/"
I had similar trouble mounting the USB stick which also returned an error message (forgot what it was) but I went via the terminal "mount" command an et voila the USB is mounted!
Is this a bug?