[O] member-ignore-case: Wrong type argument: stringp, nil

[Vikas Rawal]

I get this message when trying to export an org file (with embedded source code 
blocks) to latex:

member-ignore-case: Wrong type argument: stringp, nil

How do I go about figuring out what exactly is going wrong?

I have tried to isolate the problem by removing stuff from the file, to see 
when does the problem go away. Some source code blocks seem to cause it. If I 
remove them, the problem goes. But there is nothing in those code blocks.. For 
example, the one below is giving me trouble. 

#+NAME: australiafabainst
#+BEGIN_SRC R :results output graphics :exports results :file 
australia-faba-instability.png :width 1200 :height 700  :type cairo :family 
serif :session pulses

## Some R code here to make a graph

#+END_SRC

But there are many others like this, which are not giving any error.

Vikas