I recently supplied some Mifare classic 4 Byte UID cards to a customer of ours. None of the batch work.
They register with the customers reader at reception, they work on the contactless kiosk but then they wont work the turnstile to access the changings rooms etc.
I visited the site and took ten different Mifare classic cards with me from ten different batches. Every single card worked perfectly.
When you touch the cards that don't work to the turnstile reader you hear a beep but it remains red, it wont open. The read range etc seems fine. My phone app says these cards are genuine NXP Mifare cards but I am suspicious as I asked the customer to also activate a compatible card and it behaved in the same way as the problematic batch. It activated the kiosk etc but not the turnstile.
I have ruled out the reader picking up only 9 or ten digits reversed HEX to decimal numbers as the readers read both. On the other test cards that I successfully tested, some had a decimal UID of 9 digits and some ten.
Does anybody have any idea why these cards that appear to be genuine NXP Mifare classic are not working? Is it possible that a part of the chip that talks to the turnstile reader is damaged or corrupted? Its very strange that all of the Mifare classic cards I try from different batches work perfectly but these don't.
Any advice would be very much appreciated.
Thanks in advance.