Controling a LIGHBOX from another LIGHTBOX can cause problems and it is not easy to work in this way.
Are you trying to generate a CUSTOM-SITE-MENU on the very top of your site?
You will have to do it on the → MASTER-PAGE.
This page is a speacial page, which shows up and is active on all of your pages, where you have activated the HEADER.
And once you have opened a LIGHTBOX → why you would like to open a second one?
To be able to generate a → SUB-MENU ?
Why not generating the SUB-MENUS inside the LIGHTBOX itself → for example → by using a MUSTI-STATE-BOX ?
Or even generating a → SUB-SUB-MENU ??? → Which would open a further LIGHBOX?
And next time, when you are describing your issue, try to be more detailed with your description and imgages in most cases can tel more then a whole roman of description.