mit-scheme swank backend reports: error in process filter: Can't find suitable coding-system

mit-scheme fails to startup:

It reports:
error in process filter: Can't find suitable coding-system

--------------- Scheme Version: 9.1.1

--------------- Slime Version: 2012-01-06

--------------- Relevant .emacs config:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; SLIME ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; (setq inferior-lisp-program "/usr/bin/sbcl") ; your Lisp system
(setq inferior-lisp-program "/usr/local/bin/scheme") ; your Lisp system
(add-to-list 'load-path "~/slime/") ; your SLIME directory
(require 'slime)
(slime-setup '(slime-fancy))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; mit-scheme ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; mit-scheme swank backend config
(setq slime-lisp-implementations
      '((mit-scheme ("mit-scheme") :init mit-scheme-init)))

(defun mit-scheme-init (file encoding)
  (format "%S\n\n"
   `(begin
     (load-option 'format)
     (load-option 'sos)
     (eval
      '(construct-normal-package-from-description
        (make-package-description '(swank) '(())
      (vector) (vector) (vector) false))
      (->environment '(package)))
     (load ,(expand-file-name
      "~/slime/contrib/swank-mit-scheme.scm" ;<-insert your path
      slime-path)
    (->environment '(swank)))
     (eval '(start-swank ,file) (->environment '(swank))))))

(defun mit-scheme ()
  (interactive)
  (slime 'mit-scheme))

(defun find-mit-scheme-package ()
  (save-excursion
    (let ((case-fold-search t))
      (and (re-search-backward "^[;]+ package: \\((.+)\\).*$" nil t)
    (match-string-no-properties 1)))))

(setq slime-find-buffer-package-function 'find-mit-scheme-package)
(add-hook 'scheme-mode-hook (lambda () (slime-mode 1)))

-------------------
Debugger Backtrace

Debugger entered--Lisp error: (error "Can't find suitable coding-system")
  signal(error ("Can't find suitable coding-system"))
  error("Can't find suitable coding-system")
  (or (find (symbol-name ...) candidates :test (lambda ... ...)) (car candidates) (error "Can't find suitable coding-system"))
  (let ((candidates ...)) (or (find ... candidates :test ...) (car candidates) (error "Can't find suitable coding-system")))
  slime-repl-choose-coding-system()
  (let ((slime-current-thread t) (cs ...)) (slime-eval (\` ...)))
  (let* ((--cl-rest-- ...) (package ...) (prompt ...)) (setf (slime-lisp-package) package) (setf (slime-lisp-package-prompt-string) prompt))
  (progn (let* (... ... ...) (setf ... package) (setf ... prompt)))
  (destructuring-bind (package prompt) (let (... ...) (slime-eval ...)) (setf (slime-lisp-package) package) (setf (slime-lisp-package-prompt-string) prompt))
  slime-repl-connected-hook-function()
  run-hooks(slime-connected-hook)
  (let ((args ...)) (when-let (name ...) (unless ... ...)) (slime-load-contribs) (run-hooks (quote slime-connected-hook)) (when-let (fun ...) (funcall fun)))
  (let ((slime-dispatching-connection connection) (slime-current-thread t)) (destructuring-bind (&key pid style lisp-implementation machine features version modules encoding &allow-other-keys) info (slime-check-version version connection) (setf ... pid ... style ... features ... modules) (destructuring-bind ... lisp-implementation ...) (destructuring-bind ... machine ...) (destructuring-bind ... encoding ...)) (let (...) (when-let ... ...) (slime-load-contribs) (run-hooks ...) (when-let ... ...)) (message "Connected. %s" (slime-random-words-of-encouragement)))
  slime-set-connection-info(#<process SLIME Lisp> (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1")))
  apply(slime-set-connection-info (#<process SLIME Lisp> (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1"))))
  (lambda (&rest more) (apply (quote slime-set-connection-info) (append ... more)))((:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1")))
  funcall((lambda (&rest more) (apply (quote slime-set-connection-info) (append ... more))) (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1")))
  (progn (set-buffer (symbol-value G50298)) (funcall (symbol-value G50299) result))
  (if (symbol-value G50299) (progn (set-buffer ...) (funcall ... result)))
  (let* ((--cl-rest-- rand-50296) (result ...)) (if (symbol-value G50299) (progn ... ...)))
  (cond ((eql op-50295 ...) (let* ... ...)) ((eql op-50295 ...) (let* ... ...)) (t (error "Elisp destructure-case failed: %S" tmp-50297)))
  (let* ((tmp-50297 G50294) (op-50295 ...) (rand-50296 ...)) (cond (... ...) (... ...) (t ...)))
  (lambda (G50298 G50299 G50294) (let* (... ... ...) (cond ... ... ...)))(--buffer-- --cont-- (:ok (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1"))))
  apply((lambda (G50298 G50299 G50294) (let* (... ... ...) (cond ... ... ...))) --buffer-- --cont-- (:ok (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1"))))
  (lambda (&rest --cl-rest--) (apply (lambda ... ...) (quote --buffer--) (quote --cont--) --cl-rest--))((:ok (:pid 8271 :package (:name "(user)" :prompt "(user)") :lisp-implementation (:type "MIT Scheme" :version "9.1.1"))))
  slime-dispatch-event((:return (:ok (:pid 8271 :package ... :lisp-implementation ...)) 1) #<process SLIME Lisp>)
  slime-process-available-input(#<process SLIME Lisp>)
  slime-net-filter(#<process SLIME Lisp> "000083(:return (:ok (:pid 8271 :package (:name \"(user)\" :prompt \"(user)\") :lisp-implementation (:type \"MIT Scheme\" :version \"9.1.1\"))) 1)")