The Racket 5.1 release announcement at https://blog.racket-lang.org/2011/02/racket-v51.html and https://download.racket-lang.org/v5.1.html links to http://blog.racket-lang.org/2010/12/racket-version-5.html ([“Rebuilding Racket’s Graphics Layer”](https://web.archive.org/web/20101211053922/http://blog.racket-lang.org/2010/12/racket-version-5.html)—thanks to the Internet Archive), which is currently giving a 403 Forbidden error.
The Racket 5.1 release announcement at https://blog.racket-lang.org/2011/02/racket-v51.html and https://download.racket-lang.org/v5.1.html links to http://blog.racket-lang.org/2010/12/racket-version-5.html (“Rebuilding Racket’s Graphics Layer”—thanks to the Internet Archive), which is currently giving a 403 Forbidden error.