exceeded MAX_ALLOCATED_DESCS while trying to open file

Hi,
Using postgres 9.2, I created a FOREIGN TABLE on a csv file. It works.
But I need to change the structure of the data and I created several sql
select using union, like
select .... from .foreign table... where...
union
select .... from .foreign table... where...
union
...
It works for the first 10 select but then I get
ERROR: exceeded MAX_ALLOCATED_DESCS while trying to open file
"/srv/www/data/antidote/registre.csv"

What is it MAX_ALLOCATED_DESCS? and how can I modify it without changing
the code and re-compile? I tried using postgref.conf but this parameters
is not recognize.
thanks
steve