I've just had pretty much the same experience on an Android tablet. I have a valid account, and have been synchronizing my notes. However, for some reason Evernote wasn't syncing. The notification is very feint on Android, down in the lower left corner, in dark grey on black. I tried to manually sync but that failed. So I re-booted the tablet to see if that would fix the problem, but the sync still failed. At least this time I got a notification via the Android notification bar, and opened it. This told me that the authentication had failed, I have no idea why as I had not changed the password. But it provided a "lost password" option, presumably to reset the password, so I opted for this in the hopes it would fix the problem. On following the lost password option I was asked to enter the account email, which I did. I then received an email with a link to reset the password, which I followed and set a new password. I then ran Evernote again, entered the new password and - all my recent notes have gone. So, if Evernote fails to sync on Android because of some account problem, expect to loose your local changes.