Hi
Did a fresh install in a new folder and installed from zip file. Problem solved. Not sure why this happened.
I did have one other component installed in the problem site, but can't see how it's related, even though my logic tells me that it must be that additional component that somehow caused the issue because the rest of the site is a vanilla install of Joomla.
(Extra component was blank hallo world component with only a single front page view, so I can't see how this would impact the installation of SEBLOD.)
All good now.
SEBLOD is a very useful component. I am just starting to scratch the surface.