Didn't want to hijack the thread but in case someone can tell me: Why doesn't this itinerary work (with the same error as OP)
ORD-OKA (UA, NH)
SIN-ORD (EVA)
Is it because HND-OKA is on NH and it needs to be completely star alliance? I guess I can test it but I still need to stupidly go from HND to OKA somehow with the luggage.
Edit: still can't even if I do ORD-HND (UA), SIN-ORD (Eva)