Thanks again Tom.
I have now succeeded in running Xerte on PC, both back and front ends. I know it works.
With Mac I'm in the same place I was: admin page works, user page doesn't.
I have also experienced something unusual with Xerte hosted online. I used to run 3.9 without any problems, but after a php upgrade to cater for a new Moodle version, it didn't work any longer. Deleted installation, installed again (through CPanel/Softaculous) and I get a database failed to upload message, both in admin and user pages. I have now installed 3.10: same problem. I would have thought that an automated script installer like Softaculous would not produce such results. In short, I'm very happy that at least I have Xerte on a local network, but very surprised that I cannot run it on Mac or online,