Greetings.  I've been having problems lately in exporting Org-Mode source-code
documents to HTML and/or PDF.

I'm running Org-Mode 7.7 with Emacs 23 on 64-bit linux (Fedora 15).

I've appended a document that exhibits at least some of the problem.  The
problems are similar to the problem described at:

    http://comments.gmane.org/gmane.emacs.orgmode/45316

and can *sometimes* be circumvented by executing org-reload.

In the particular example shown below, the HTML export works as expected, but
the PDF export fails with message:

    org-export-latex-preprocess: Wrong type argument: stringp, nil

By the way, everything worked fine in the example until I added the last
source block:

    #+begin_src R

      x

    #+end_src

I tried using what I take to be the latest version of Org-Mode:

    Org-mode version 7.7 (release_7.7.290.g65d05)

but that only made things worse.  I tried an HTML export with this version, and
it generated a horrendous-looking message that begins with:

org-babel-R-evaluate: Wrong number of arguments: #[(session body result-type
result-params column-names-p row-names-p) Æ=}...

followed by a bunch of stuff containing enough non-printing characters that
it's hard to reproduce in email, and ending with:

...org-mode/lisp/ob-R.elc" . 9734)], 5

I'd welcome any help/advice that anybody can provide.

Thanks,

-- Mike

########## Sample file that exhibits some export problems

#+TITLE: This is a test

#+AUTHOR: Michael Hannon
#+email: jm_hannon@yahoo.com

#+BABEL: :session *R* :cache yes :results output graphics :exports both :tangle yes

* Getting Started

** Batch Mode


#+begin_src R :exports code

pdf("xh.pdf") # set graphical output file
hist(rnorm(100)) # generate 100 N(0,1) variates and plot their histogram
dev.off() # close the graphical output file

#+end_src

If we put the code above in a file called =z.R=, we can execute the
code from the command line via: =R CMD BATCH z.R=


#+begin_src R
  
  x <- c(1, 3, 5)
  
#+end_src

#+begin_src R

  x[3]

#+end_src

#+begin_src R

  q <- c(x,x,8)

#+end_src

#+begin_src R

  x

#+end_src