I had the same problem on OSX 10.6.8 (10K549), after upgrading to Evernote 5.0.6. Uninstalling and reinstalling, repeatedly, failed to correct the problem. After removing Evernote with CleanApp, I resorted to using Time Machine to restore Evernote version 5.0.4. I was then able to successfully log in and reload my data. Danielle, as an alternative, you could try the web interface until Evernote can get this bug identified and corrected.