Problem solved. I found a setting in the theme (Story) that relates to an obscure setting that a number of people on the web have found confusing, including me. The main problem is that it creates a fake or misleading and erroneous trail to the error I posted above: You need to make this file writable before you can save changes. See the Codex for more information".
I am posting the solution here to prevent other people being led up the garden path in relation to the specific example that I was looking at, which I am assuming relates solely to the Wordpress\Story (Pexeto) theme but it might also include others.
The problem affects all "Blog Posts" at the bottom of every page, where the following heading appears: "YOU MAY ALSO LIKE" (aplicable to retailing websites as in shopping alternatives). The solution is very simple. In the Wordpress Dashboard, select: Dashboard\Story\Story Options\Post & Page Settings. Then select the Blog Posts tab and look for RELATED POSTS SECTION and switch: Show related posts after post content to OFF. Problem solved!