Hello, ZwerOxotnik!
Error occured on loading a savefile.

Error while running event useful_book::on_configuration changed A script command already exists with the name: tl stack traceback: [C]: in function 'add_command'
useful_book__/models/useful_book.lua: 1557: in function, 'compile_all_text'
useful_book_ /models/useful_book.lua: 1594: in function 'update_global_data'
__useful_book _/models/useful_book.lua: 1608: in function 'on_configuration_changed'
__zk-lib/static-libs/lualibs/event_handler_vZO.lua: 111: in function, <_zk-lib__/static-libs/lualibs/event_handler_vzo.lua: 108>

Thank you.

A... oh... it's a bit strange, I can fix this specific case, I guess. For some reason, there are 2 of the same command name.

It should work with your save now. Perhaps, some mod added a similar command with the same name.
https://mods.factorio.com/mod/useful_book/downloads

I'd like to get your save (it's not necessary), because, perhaps, I made a mistake in previous versions that might a cause a desync in the new version in some cases.

So, perhaps, as you load the game in multiplayer and invite someone, then you might encounter a desync.
However, if you load your save and save it again and load it, then it should work fine.