We have read carefully the discussions and watched the videos on "Search/Login" particle.
We have a Search page for the results in a hidden menu.
We have enabled the particle module on "header-search" position, placed in "Navigation" section of our Medical template.
As it is multilingual site, the "Menu" particle is attached to "mainmenu-fr" for outline FR, and "mainmenu-en" for outline EN.
I enclose an image of the layout.
Despite these settings, when we enable the Search/Login module, the site can't be refreshed and it finally goes to Error 500.
I enclose credentials and url.
Many thanks for your help and ideas.