There is no .httaccess file anywhere, not even F:/WebDev/mysite/v005wp/. When I have manually added the .htaccess file (with the following text recommended on https://codex.wordpress.org/htaccess#Basic_WP )
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
The same error is returned.
(In XAMPP mod_rewrite has also been enabled in conf/httpd.conf.)
This happens both locally and on the live server where again, I have other, older versions of WP running without a problem. I do not believe this to be a server issue.
Again - this seems potentially significant - my wp-includes/vars.php file does not match the code on http://codex.wordpress.org/Using_Permalinks#Fixing_.htaccess_Generation_Issues
I'm using wp v3.9.1