2014/1/7 Nick Dokos <ndokos@gmail.com>
Run latex on /tmp/orgtex11506Npy.tex from the command line and look for
errors.

Many thanks Nick. I did not think about  it. 

But it is more and more strange: it seems to be no error : Have a look ;

joseph@crunchbang:/tmp$ latex orgtex11506Npy.tex 
This is pdfTeX, Version 3.1415926-2.5-1.40.14 (TeX Live 2013)
 restricted \write18 enabled.
entering extended mode
(./orgtex11506Npy.tex
LaTeX2e <2011/06/27>
Babel <3.9f> and hyphenation patterns for 78 languages loaded.
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/article.cls
Document Class: article 2007/10/19 v1.4h Standard LaTeX document class
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/size10.clo))
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/color.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/latexconfig/color.cfg)
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/dvips.def)
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/dvipsnam.def))
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/inputenc.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/utf8.def
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/t1enc.dfu)
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/ot1enc.dfu)
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/omsenc.dfu)))
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/fontenc.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/t1enc.def))
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/latexconfig/graphics.cfg)))
(/usr/local/texlive/2013/texmf-dist/tex/generic/ulem/ulem.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsmath/amsmath.sty
For additional information on amsmath, use the `?' option.
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsmath/amstext.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsmath/amsgen.sty))
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsmath/amsbsy.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsmath/amsopn.sty))
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/textcomp.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/ts1enc.def
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/ts1enc.dfu)))
(/usr/local/texlive/2013/texmf-dist/tex/latex/marvosym/marvosym.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/wasysym/wasysym.sty)
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsfonts/amssymb.sty
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsfonts/amsfonts.sty))
No file orgtex11506Npy.aux.
(/usr/local/texlive/2013/texmf-dist/tex/latex/base/ts1cmr.fd)
(/usr/local/texlive/2013/texmf-dist/tex/latex/wasysym/uwasy.fd)
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsfonts/umsa.fd)
(/usr/local/texlive/2013/texmf-dist/tex/latex/amsfonts/umsb.fd) [1]
(./orgtex11506Npy.aux) )
Output written on orgtex11506Npy.dvi (1 page, 352 bytes).
Transcript written on orgtex11506Npy.log.

End of quotation. I do not quote the log file, it would be rude, it is very long. 

I wonder if the  "restricted \write18 enabled." betrays something helpful ? 

Best wishes, and thanks for your kind help,

Jo.