On SBCL, the error looks like this:
error opening #P".../client-info.sexp": No such file or directory
On Clozure CL, it looks like this:
> Error: No such file or directory : #P".../client-info.sexp"
Other implementations present similar error messages.
If you are encountering this problem, evaluate this:
(ql-http:fetch "http://beta.quicklisp.org/client/2014-01-28/client-info.sexp" (ql-setup:qmerge "client-info.sexp"))
If you aren't having any problems, there's no need to use this bit of code.
After fetching client-info.sexp, you should be able to evaluate (ql:update-client) without encountering any errors.
I've uploaded a fixed version of the client that compensates for the missing file, so future updates should not signal this missing file error. If you have any problems or issues with Quicklisp, please feel free to email me, email the mailing list, or discuss it on freenode #quicklisp.