Non linear Poisson Equation

Hello! I'm trying to solve Poisson equation with Sfepy in a very simple domain, but I found some problem:

1. I need triangular mesh on a rectangular/square domain
2. I have null von neumann conditions ( and I omitted them in boundary condition) like in the
   discussion https://groups.google.com/forum/#!searchin/sfepy-devel/null$20von$20neumann/... 3)I know that this problem have many convergence problem, in one of this case is the simulation successful? Or I find some error?

I don't know because the simulation is successful but in the postprocessing the result isn't correct I attach the problem description file too. If you want I would like some advice about my problem Thank you very much -Francesca