dpcschalkwijk Kindly try and update to latest version of zentools module to see if it helps as the same comes with various improvements and bug fixes from here. As of currently, You seem to have quite older version installed
Also, You may update your template to latest version i.e.1.4.2 from here (The download link for latest version of zentools module is also seen here)
Would suggest to also take backup of your site before performing aforesaid steps, in case rollback required whilst facing any issues e.t.c