As yet another update:
I think I've figured why my old projects were not working.
First, Xerte update renames all the folders for the old projects to something Number-User-Nottingham on the server but not on the Xerte Workspace
While the system was running in very slow mode I've tried to create one project many times.
The result was that, once it eventually showed up I had six projects with the same name that I then deleted 4 of them. As they all had the same name I've deleted them in no particular order, using the workspace interface.
When I fresh installed Xerte and kept the User-Files folder and re-generated the upgrade it renumbered my projects again. I don't mind the renumbering but somewhere inside the projects, the references to pictures were still pointing to a folder that no longer existed. When I manually renamed the project folder on the server to match the expected location inside the project it then started to work again.
Regards,
Marta