trouble exporting just one subtree while using babel and R code blocks

["Christopher W. Ryan" <cryan@binghamton.edu>]

I have a long cumulative org file that contains work related to a series
of studies. Each first-level subtree (*) is a new study. I need to be
able to export any given first-level tree on its own, with an output pdf
file name different from the main org filename, and with a title perhaps
different from the * headline. And I need to execute R code as it
exports. I am running org-mode 7.7 on Windows XP

A sample org file to illustrate the problem looks like this:

------------------------------------------

* goodbye

foo foo

* Hello
:PROPERTIES:
:EXPORT_FILE_NAME: TestMyBabelSetup
:EXPORT_TITLE: foobar
:EXPORT_AUTHOR: Christopher W. Ryan, MD MS
:RESULTS: output
:EXPORTS: both
:END:

foo

#+begin_src R
rnorm(3)
#+end_src


--------------------------------------------

When I export the whole file to pdf, everything works fine.

But if I try to export just the * Hello tree, then I get an error:

 Args out of range: "", -1, 0

If I remove anything relating to R and babel from the * Hello tree,
leaving just this:

-----------------------------------------------
* goodbye

foo foo

* Hello
:PROPERTIES:
:EXPORT_FILE_NAME: TestMyBabelSetup
:EXPORT_TITLE: foobar
:EXPORT_AUTHOR: Christopher W. Ryan, MD MS
:END:

foo

-------------------------------------------------

then exporting just the * Hello treee works as expected.

I'm stumped. What am I doing wrong?

Thanks.

--Chris
-- 
Christopher W. Ryan, MD, MS
SUNY Upstate Medical University Clinical Campus at Binghamton
425 Robinson Street, Binghamton, NY  13904
cryanatbinghamtondotedu

"Once we recognize that we do not err out of laziness, stupidity, or
evil intent, we can liberate ourselves from the impossible burden of
trying to be permanently right. We can take seriously the proposition
that we could be in error, without deeming ourselves idiotic or
unworthy." [Karen Schulz, in Being Wrong: Adventures in the Margin of Error]