Maybe check the console for you browser, that would probably give a more detailed error

I'm aware of this tool, I was thinking more about a behaviour like this : https://youtu.be/f9pYZ9lf7oU?si=Q9uZjvYXnG93YRyq&t=87 (Empire Earth Scenario Editor)   Yeah, I know :p Just telling what could be nice, no big deal

Have you done this at the end? Maybe it would fit with something like what I just proposed.   I agree https://gitea.wildfiregames.com/0ad/0ad/issues/5672 should be closed. It makes no sense to have Issues stating that maybe there's a problem, many versions past, reported by one person 7 years ago, when just "reinstallation might help" but there was no follow up. If there's still a problem someone will open an Issue again (or better, reopen that one).   I don't see why that would be the case, it could be implemented not substantially changing present gameplay, as remarked at the end:   Have the sound files been retrieved? Would be a shame not to get this out of the way if "even a non-technical user could get it done in less than an hour".

Try private browsing or cleaning cookies. If none of those work, I'd restart my PC. After that, you'd need to search for more specific solutions...

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