Hello, this is a forwarded bug http://bugs.debian.org/400734 from a Debian user: "man 8 mount.cifs suggests that a credentials file can only contain username and password fields. It can, however, actually also include a workgroup field. Which is important if a Windows file server suddenly stops accepting user@domain as username but insists on username user and workgroup domain." Thank you.
*** This bug has been marked as a duplicate of 4541 ***