Yay, it’s working!
However, I continue to have the same issue that’s plagued me for a long time now: If I try to use the Photopress option “use permalinks” (my preference), it doesn’t work. Clicking on the thumbnail (which should take you to the full image) merely causes the page to be reloaded (but with the correct image URL in the browser address bar!).
I have finally worked out that there seems to be some mysterious link between this permalink option and the option Link to album ("The code for inserted images can point to the image in the album or straight to a popup containing the image").
Permalinks do work – but only if I have this Link to album option set to "No".
If I want to point to the images in the album, I have to disable permalinks.
I would dearly love to be able to have both permalinks as well as the album link enabled and working correctly.