Lstlisting in beamer presentation

I have found the problem. The grey area displayed is for the caption of the code. Apparently it is grey because of the beamer style I am using.

So, setting captionpos to n in lstset fixes the problem.

Instead of using this trick, you can just add the option fragile in your frame

    Calcul Symbolique (\textit{calcul formel})
            \item Algorithme sur les objets mathématiques

enter image description here