>> 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.
>
>
> Could I ask you to provide the entire backtrace for both errors?
> 
> M-x toggle-debug-on-error RET
> 
> The backtrace might contain information about the exact place where a
> string is expected. If you can't copy it into the email program save
> to disk + gzip + attach should do the trick.

Hi, David.  I've attached the backtrace for:

    Org-mode version 7.7 (release_7.7.304.g9da4)

(I was traveling when I worked on this previously, and my environment has now
changed.  The version I'm using now exhibits the same kind of error.)

Thanks,

-- Mike