I am a huge fan of Amazon's Simple Storage Service (S3). It's allowed me to host Quicklisp data cheaply and reliably for a long time.
However, over the past few days, I've run into some permission problems with the Quicklisp S3 objects, and the latest Quicklisp dist update is damaged as a result. Files that seem to be present are not actually available for download, and I'm not sure why.
I don't recommend updating your Quicklisp dist until this problem is resolved. I hope to fix it within the next 24 hours. Sorry for the inconvenience!