Yes, I know all this things, and there is no problem with the database restore.
What I am trying to explain is that with my investigations, I know that the problem comes from the database
I've installed a new forum ( with a new BDD ) and changed the prefix, so I put my old database prefix : same problem.
Same files, but I changed the prefix to the new installed base : no problem !
So it comes froms the database. But where ?
PS : The frenchs communities are down, in those times... I've asked, but not any answer.