I'm not sure if this is the right list to post this, but I'll give it a shot here, and see where I should report this.
The problem seems to be the website's hosting, which appears to be provided by Google, which blocks access from certain countries in accordance with US law (with the error message "403. That’s an error. Your client does not have permission to get URL / from this server. That’s all we know."). This would not surprise me if LilyPond was not a GNU project, but it's a bit off at the moment, to say the least.
What I would want to know if this is something the team cares about, and where I should discuss this.