I must have made a big mistake while trying to install another website under www (multisite). I am no more able to open my zenphoto sites. I get the following message:

*Zenphoto has detected a change in your installation.

Zenphoto 1.4.8[3e3fac42b5] has been copied over an unknown release.
The change detected is critical. You must run setup for your site to function.*

I tried to run a setup under http://my site/albums/zp-core/setup.php?autorun=gallery&xsrfToken=7834275680340a19e768450aced5dd4fe6f240eb

or simply

under http://my site/albums/zp-core/setup.php

but nothing happens.

What to do? I would be very grateful for your help.

The url to run setup is thepathtoyourinstall/zp-core/setup.php. "albums" is not part of that, unless that is your indeed your install path.

By default Zenphoto protects setup files that first need to be unprotected. Look at zp-core/setup. See if there are non php files and rename them manually.

If you now have indeed two installs of Zenphoto or even different CMS in the same root folder there is most likely a conflict. You will have to move the Zenphoto install to a subfolder. Info about moving installs here: https://www.zenphoto.org/news/moving-and-changing-existing-installations/