switch to the āscā REPL tab (next to the āmatronā tab which is selected)
and enter ;restart
that will show you any supercollider errors, including ERROR: Duplicate class [blabla]
BASICALLY
make sure there are no duplicates of any .sc files anywhere in code/
(like code/_somewhere_/lib/THING.sc and code/_else_/lib/THING.sc)
BTW: while Librarian is a cool thing to have made, it is also dangerous, b/c it does not encourage you to inspect the stuff you are putting on your norns filesystem. weāre in the slow process of developing some analogous management tools that will be more careful about creating duplicate engine classes and other stuff.
in the meantime we are trying to devise some better error messaging. weāre aware that the duplicate-engine problem is a PITA and there has been much heated discussion about it on many channels for a while. conclusion: the least-bad way for now, is for both script authors and script consumers to exercise some care and diligence when distributing / installing engines or other .sc files. the former should clearly document when their .zip includes .sc files; the latter should read the documentation.