Thanks for your reply, but if I look at the properties of wp-content, I see its owner is charles, but “Others” can “Create and delete files” so I can’t see what is wrong.
With regards to your alternative suggestion, I have now created a new directory inside wp-content/themes but can see no way in the dashboard (4.5.3) to “Activate” it. How do I do this last step please?
While I am grateful for your help in specifying a work-around, I still maintain the WP-core should provide more information at the time of error, for example what directory is being created, and if possible what the current user is.
