Error when running org-babel-execute-buffer -- Wrong type argument: consp, nil

[Ista Zahn <izahn@psych.rochester.edu>]

Hi,
I recently upgraded to version 7.3 (from 7.01), and discovered that
org-babel-execute-buffer no longer works, returning "Wrong type
argument: consp, nil". This behavior is exists even with the simplest
of examples, such as

#+begin_src R
2+2
#+end_src

and persists even when I reduce my .emacs file down to a bare minimum of

;;Set up org mode
(require 'org-install)
(add-to-list 'auto-mode-alist '("\\.org$" . org-mode))
(define-key global-map "\C-cl" 'org-store-link)
(define-key global-map "\C-ca" 'org-agenda)
;; Enable R, latex, lisp support
(org-babel-do-load-languages
 'org-babel-load-languages
 '((R . t)
   (latex . t)))

org-babel-execute-src_block works. If all blocks have been evaluated,
then running org-babel-execute-buffer  works (even if  a block has
changed), although it returns a message saying "Invalid function:
org-babel-map-src-blocks" (I don't know if this is related or not). In
other words, org-babel-execute-buffer works to update blocks that have
previously been evaluated, but fails when the buffer contains
unevaluated blocks.

This is with org version 7.3, and I get the same behavior using emacs
version 23.2.1 and emacs version 24.0.50.1

Any help will be appreciated.

Best,
-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org