I have the same problem. I was working in my Mac Evernote app, when an error popped up and I had to close the program. When I reopened it, there were no notes. All notes are still there on the online platform. I only have one account, one set of username/password, so its not really possible to be logged in under a wrong UN/Pw. Regardless I tried signing out and singing back in, restarting everything, synchronizing. Any other ideas?