I'm currently doing some modifications to zpBootstrap. Not sure about rewrite - at least I didn't add any.
Login screen came up. After the login there was only 403 for all users. BTW the 403 error came up immediately after activating the plugin and saving the changes. The reload of the admin page never happened.
As I said, to fix this I disabled the plugin in the database with phpMyAdmin and everything was fine again.
A little later however I got that message about a change in the installation being detected and to run the setup script again. Setup gave an an error and couldn,t connect to the database. I then discovered that the password on the database no longer worked. I created a new user in the database, entered the new settings in setup and everything has been fine since. I'm no MySQL specialist so I have no idea what went on there. I remember reading, however, that some version of MySQL apparently has a bug that can cause the password to not work any more.
Any way, it's working now.
I'm not sure what the exact reason for all this is. My assumption at first was that when the gallery is set to private and at the same time show_not_logged-in is active, that this will cause some kind of conflict because the gallery can only be seen by someone who is logged in.
When I get some time I'll setup a second zenPhoto installation and see if this happens again under the same circumstances on the same server.