He finally found a solution on Apple's forums, that might be usefull for other people:
You need to go to
/Library/Audio/Plug-ins/Components
and remove all the plugins that might be in there... you'll also need to do the same in your local user /users/*yourname*/Library/Audio/Plug-ins/Components.
[note: remember to keep a copy of any file you might remove... they might be used by some other application]
