I found that access to your documentation via that URL is currently broken and yields a HTTP 404 error. Evidently the relevant page has been moved to the below address, but without leaving a redirect:
This leaves incoming links dangling, for example links from Wikipedia, etc.
I have not checked whether this is a general problem that might affect many more pages beyond just this one. I imagine it could be the case that this issue extends beyond MIT/GNU Scheme to many other GNU software documentation pages and gnu.org URLs. I think you would be in a better position to check that. Whatever its scope, I do believe this is a bug worth fixing, because, as Tim Berners-Lee put it, "Cool URIs don't change":