This is unacceptable. I am never able to check in online for my outbound flight, always get the message "This is not a boarding pass". Things always work well to my friend in the same PNR though. I have already had my passport scanned at the airport a number of times, talked to UA agents, but nobody is able to give me a reasonable answer. If this is random, as people say in some threads, I am in a very very very long string of bad luck. If this is a system glitch, I cannot imagine why UA hasn't figured it out yet. Sorry if my English is not good enough to express all my frustration right now.