Yea, Evernote did not like the null value for the computer name. Not sure if this is fixed in recent versions, or if it will be fixed. I would assume EN is using the value to populate a default value for the device you are syncing... I would prefer it asks, even if a null value is found.
I believe this problem may have something to do with a hardware/device check on the device you are using -- in this case, a Mac with a device UUID. I was getting this exact error. Since I was using two factor auth on Mac OS X 10.9 (on a Retina 15) I thought I would turn off two factor auth. No go. Since I could log in with other computers running 10.8.x and devices, I figured it was device specific. I deleted the app and reinstalled. I killed the data in ~/Library/Application Support/Evernote/*. I used AppCleaner to make sure all was gone. No solution. So I turned on the log and watched as I