Error: “ chgrp invalid group 'domain users' ” when setting up shares

Question

I'm following this tutorial: Samba Shares with Active Directory Login on Ubuntu 12.04 , and when I enter the command: chgrp -R "Domain Users" /sharing/ , I get " chgrp invalid group 'domain users' ". If I run wbinfo -g, the group is in the list.

I'm running 14.04 instead of 12.04 and samba 4.1.6, when I installed the other packages, smbfs was unavailable but cifs-utils was recommended, so I installed it.

Sorry if this is a simple (stupid) question, but I'm really new to the linux environment.

Thanks, Charlie