[Tails-testers] TAILS 3.1 does not start up

Hi,
I am using tails 3.02 en works perfect, now i tried to use TAILS 3.1 but i keeps saying start in 4 sec then counts down to zero, and keeps on doing that, i tried 5 different laptops and 3 different usb sticks.
Can you help me?All laptops are 64b
thanks best regards,  Gerard