I see that there is a recent change that means that client-as-string is called from create-request-
handler-thread. This breaks for Lispworks users, as client-as-string is only defined for platforms that use usocket (or strictly speaking, for platforms which are not lispworks :-)

The following implementation of client-as-string seems to do what's required for Lispworks:

#+:lispworks
(defun client-as-string (socket)
  "A helper function which returns the client's address and port as a
   string and tries to act robustly in the presence of network problems."
  (multiple-value-bind (address port)
      (comm:get-socket-peer-address socket)
    (when (and address port)
      (format nil "~A:~A"
              (comm:ip-address-string address)
              port))))