Happened to me too this morning. Random error messages for no good reason. Trying to book ex-TPE ticket....
1. Wouldn't let me choose HKG as a destination on my return flight (TPE HKG HND HKG TPE)
2. Closed Chrome, tried again ... it worked. Then error message after choosing second or third flight.
Flight is in 2016, so I'll wait a few days and try again.