OK found the solution myself after much searching and trail and error, and as no forum administrators are likely to help here's the solution.
Not sure if this first step was necessary in the end, be aware you will loose all your users and shares by doing this.
apt-get purge zentyal-samba
apt-get install zentyal-samba
then once you've recreated your shares and users
chown -R Administrator:adm /<shared directory>