DMCS theme version was already to latest version of 1.1.22 and RevSlider plug-in version was already to latest version of 5.2.5.4
Un-installing the RevSlider plugin and reinstalling didn’t fix the error. What I did next was to re-install WordPress and then re-import the dmcs.zip theme. After importing the dmcs theme I installed and activated the theme required plugins.
The error is no longer appearing after going through the full WordPress, theme, and plugin reinstall.
not sure why the error occurred during the first installation.
