I experienced this.
I missed the flight not because I was late, but looking into the wrong day. Here is the scenario.
I had mind set that i always travel for company business on Sunday and next day (Monday) will be at work. Without hesitation, I knew the week that I need to travel and I did the web check in on Saturday. The system failed me after a couple of attempts. Upon checking the eTicket again, the date is correct but the travel day was on Saturday. Goodness me!!! I was really panic and called the airline for next flight. Was quite a struggled in getting the flight and air fare made the difference. No show fee imposed. As this is company trip, i really had to be thick skin and called up my boss to explain my situation.
This is a lesson learnt for me. From then on, each travel i will check, and check on the date of the travel.