I activated 2-factor authentication yesterday from my work computer (a PC). When I returned home and started Evernote on my MacBook Pro, I was met with the same challenge as others in this thread: Evernote for Mac would not accept my password. Using AppCleaner to remove Evernote thoroughly, then downloading the app via Evernote.com and re-installing worked for me, though not without hitched. The initial sync hung with 14.1MB remaining. After a Force Quit and re-launch, Evernote finished the job and everything seems to be all right.