https://www.evernote.com/Devices.action shows 2 devices
current mobile device and web
I just installed the mobile app again and gave it another try and mysteriously it seems to have started working again. No idea why, I did not change anything.
My wife couldn't cannot even log into the web app from her PC, but was able to login from her phone, so removed her devices there.
so it eems even the web app limits you from logging in from only 1 device. So if you have logged into website form more than 1 devices, you get locked out.