Yesterday I put up an update to the Quicklisp client software. Unfortunately, it was broken on any SBCL older than 1.0.44, which turns out to cover a lot of SBCL users, including people who got SBCL for Windows from www.sbcl.org and people who get SBCL from their Debian, Ubuntu, or Red Hat package systems. To fix the problem, I've put out an updated version today that will hopefully resolve that problem.
To get the new client, you can use (ql:update-client). The new client will be loaded when your Lisp session is restarted. Please let me know if it causes any problems for you!
update If you got the bad update, and you're having trouble starting SBCL as a result, there are a few things you can try. If you have CLISP, you can use that to get the good update, and it will be used the next time you start SBCL. You can also fetch http://beta.quicklisp.org/quickstart/quicklisp-2011032000.tgz and unpack it in ~/quicklisp/.