I have turn off all SEO settings and it's still the same.
I have checked that there is no template assigned to menus as well.
I confirm that it's only when I activate the lime light template that it breaks. So it must be something link to lime light settings somewhere !
It seems that the search function also has the problem. When I make a search on certain pages it goes blank, but not on all pages ! Again, only on lime light, with other templates search works.
I have made a short screencast where I demonstrate the problem in more details: http://screencast.com/t/p2ZPi4Hk
What else can it be ??