EigenValue function


I am currently trying to solve an eigenvalue problem with the function EigenValue of Freefem++ and when the code start to launch this function, I get such kind of error:

Assertion fail : ((!this->N() || !this->M()) || !Ax.x.N() || !this->N() || &Ax.x[0] != &this->operator)
line :560, in file ./…/femlib/RNM.hpp

Is it a problem that already arrive or did I made something wrong in the code.

I thank you very much,

Maxime Fiore