Originally Posted by kgsd
I recently tried to check in online for a flight later that day, and got an error message saying I needed to get my boarding pass from an agent. (Of course the agent gave me a B boarding pass.) What are some reasons I wouldn't be allowed to check in online?
2 major causes: Rapid Rewards travel using a paper voucher requires in-person checkin. SSSS (Special Security Screening Selectee) tickets also require in-person checkin. Its also possible that your ticket originally showed SSSS but that the ticketing agent overrode the selection.
Other than those, I don't know of any other common reasons, but I am sure some exist.