I just turned my ad-blocker and pop-up blocker off for libbyapp.com then repeated the fix. But it still didn't work.
Could it be because I'm using a MacBook? Clutching at straws here trying to think of any other possibilities.
Otherwise it sounds as if Libby/Overdrive have successfully locked down the downloading of magazines.
ETA: One final attempt before I give up completely - I have been doing this on Safari, and repeated all the steps in Firefox but still didn't work.