I got a weird error at the end of OLCI, never encountered this before;
"Based on your itinerary and passport information, we're unable to complete your check-in.
Before going to the airport, please visit our website and review the Travel Documents section to learn more about the entry requirements of the country you plan to visit."

(YYZ-SFO in AC I and SFO-SNA in X on United) . I'm on a US Passport, traveled on Rogue to the US earlier in the week w/o issue, others are canadians on canadian passports.. but it wouldn't let any of us check in..
(UA Award ticket, UA says everything is fine with the ticket/PNR)

Any insight?