Menu trouble…

Hi everyone,

I can no more managed my menu: each time I try to save it I have: error 500 internal server error!! Whatever the theme I use or the version of WordPress (it was the same with the former one).
I have to say that I have 160 sub-menu or options it is big but not huge. Is somone able to help me?

I use WordPress with the theme Twenty Eleven

My site: http://www.natureetphotographie.fr