Upload paths are not working properly

Hi -
I have had some detail pages that were working perfectly well until recently. However (and this might have co-incided with a long overdue upgrade about three months ago) something strange is happening.

Images that are uploaded for certain fields are not displaying - when I check the source I often find that the path to the image is completely missing (so it only displays the filename).

I have the URL path set in 'General Settings'. I have tried various different things, such as setting custom paths and then unsetting them. I've checked everything I can think of but nothing seems to work.

One odd thing is that I'd expect old detail pages to follow suit as they are constructed 'on-the-fly' from the template file and the database, but the older records seem to work perfectly well. However, if I remove and re-upload the image it disappears (the path and the image)

Here's an example of an old record with the path and image still working (best practice logo top right): http://www.eyps.info/providers/Providerpage.php/7

And here's one that worked perfectly well until a few minutes ago when I deleted and re-uploaded the same image: http://www.eyps.info/providers/Providerpage.php/13.

As far as I can remember I haven't changed the template file, but can't swear to it. But I'd have thought it would have treated all files the same if it was the template causing the issue.

Any help would be gratefully received - it's one of those tear your hair out things which is probably perfectly obvious...