[O] Wrong type argument listp on export

[Dirk Scharff]

Hello,

I narrowed down my problem to the following short example:
* My Test Block
 This is a test
 #+source testblock
 #+begin_src python :var x=3 :exports both :results output
 print x*x
 #+end_src

executing the source-bock yields the correct result. When exporting 
this file however I get the folowing error:

Wrong type argument: listp, 3

Am I doing something wrong here?

I'm using Org-mode 7.6 (release_7.6.129.gfe0c).

regards,
Dirk.