Now it's working, thanks ! Maybe it was related to a shortcut conflict, or maybe the bug was just sitting between the chair and the keyboard as usual.
Now the syntax help works (help key) and "online" help works with Right amiga +help.
The only unknown thing (even if it seems to not disturb the program) is these 2 libs drawers (system and basic) I had to remove from the blitzlibs to install the BSS. Anyway I store them in another personal documents drawer for future illumination
edit :
Any idea to obtain the top fixed dock like on this picture, by the way ?
http://obligement.free.fr/gfx/superted25.jpg