Comment 5 for bug 1729337

Sorry, it doesn't seem to have fixed the issue. I installed the image, extras, and both headers packages. No cloud or tools (they aren't installed in our system usually).

root@client:~# uname -a
Linux client 4.4.0-98-generic #121~lp1729337 SMP Wed Nov 1 14:29:16 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

root@client:~# dmesg
... snip ...
[ 9.177979] CIFS VFS: validate protocol negotiate failed: -11
[ 9.178594] CIFS VFS: cifs_mount failed w/return code = -5

root@client:~# mount.cifs --verbose //server/share /mnt/share -o rw,user,credentials=/etc/samba/credentials.share,uid=33,gid=33,file_mode=0770,dir_mode=0770,exec,soft,noserverino,vers=3.0
domain=ourdomain
mount.cifs kernel mount options: ip=1.2.3.4,unc=\\server\share,file_mode=0770,dir_mode=0770,soft,noserverino,vers=3.0,uid=33,gid=33,user=www-data,,domain=ourdomain,pass=********
mount error(5): Input/output error

Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
root@client:~#