Thanks Eric for your kind and smart help. I have understood, thanks to you, what was my problem: in fact in my export settings, I mention some packages that are useful only when I want to export into the smf class. http://smf4.emath.fr/Publications/Formats/ that is a nice class to produce beautiful papers. But these packages produce these strange images when they are mentioned by default in the packages list.

I have to work on my configuration to solve this problem, and your emails put me on the right way. Many thanks !

Jo.