Frank Ralf wrote:
One assumes the image has been uploaded?
Yes, the very same link on the parent page does work alright.
Are subpages actually enabled for that namespace? The easiest way to check is to see if the breadcrumb link to the parent article is present on the top of the subpage.
If it's not there, subpages aren't actually enabled. They /kind of/ work, but a lot of weird things happen. It's been a while, but I think this exact thing happened to me.
To enable it for that namespace, look into the $wgNamespacesWithSubpages variable in LocalSettings.php.