Comment 17 for bug 1572132

I'm also experiencing this bug on Ubuntu 16.04.3.
I don't think Windows supports SMB 1.0 any longer due to security issues. (mount error(121): Remote I/O error)
Adding vers=2.0 or 2.1 to the mount command line options successfully mounts the share, but using rsync to back up this Windows share is not reliable if it is missing 2 files.