Had similar problem on Sunday (14th August)at Kings Cross. Tried my key on ten bikes, the first took 15 seconds to give me a red light, the next nine just three flashes each. Tried using my debit card (with loads of credit), the terminal took me through the entire casual user process before giving me the “you have been unsuccessful” message. On the verge of giving up and taking the expensive (but oh so reliable) taxi option, but had one last go with my key and got the green light. Why can’t the system just reliably give me a bike each time I put in my key? I never have any problem with my Oyster Card,getting on the tube, which presumably uses similar chip reading technology.