You have, I just mentioned it. Perhaps the 4 or 5 times I witnessed it within my own group over the last 12 years was just coincidence but I'd guess it was happening regularly myself. I only got in when it happened to me because my ten year old son was on the other side of the gate and I asked the steward who was going to look after him while I queued up at the ticket office to prove who I was (as per their instructions). I tried again at the next game and was once more faced with it not working, so I ordered a replacement. The steward said it happened sometimes. My brother on another occasion was less lucky and had to queue up at the ticket office to resolve his issue of a printed ticket not working, as was my mate when his card didn't work. He's also had the issue twice. For both my mate and me, this was halfway through seasons so the cards had been working but suddenly stopped. Sounds either like corrupted data storage or the circuit was broken inside the card but I guess it could be an access list error.