I'm having this problem too but am stuck at a different point because I followed another post to remove everything and reinstall Evernote from Mac App Store. I have Evernote 5.2.1 for Mac installed and I'm running OS X 10.8.4. On initial sign in screen I get this message whether I use my email address or username. Since it's a reinstall, I can't move on and can't see the <null> account option mentioned earlier in this thread. I can login to website without an issue. I'm a premium user and so have dual factor security and these problems all see associated with that security. I had the same before so turned it off and all was well. I want the securing on, though. September 17, 2013; 10:57 PM Update: I sorted it out as follows: 1. Logged in to the website 2. Turned off dual factor authentication 3. Logged in with email address (not user name) 4. Waited for data to replicate 5. Logged out of both local and website 6. Went to website and turned dual factor back on 7. Logged back in to local software and website successfully So far so good.