Yes, of course ... But I was sure that the problem doesn't come from here, as it work perfectly from the admin/plugin page !!
I do even worst :-) , on my test server, where I have installed the fresh e107 and lightbox, I have copied the database from my live site and ... it doesn't work !! I just need to check in the db if the address of the live site isn't in and force the server to take files from the live instead of the test server.