I had the very same problem occur again with 10.5.7 reverting to 10.4.4. I uninstalled, restarted, and reinstalled manually again. Then I logged on and saw everyone else's advice. So unfortunately I did not have the opportunity to try the methods everyone discussed here in this thread.
However, when I uninstalled Evernote in Windows's built in "Add or remove programs," I had to uninstall two separate versions of Evernote—10.4.4 and 10.5.7. So that would seem to confirm at least some of what people are saying here.
Also of note is that I always install Evernote for just my user, but updates appear to automatically install the program for all users.
Finally, when I reinstall Evernote, I am always automatically logged in and my notes are already loaded into the program. I am not a techie, so maybe this is a normal thing, but it does bother me because when I uninstall a program I expect it to remove all of my data from the computer. I wouldn't want someone else to be able to reinstall Evernote on my computer and see all of my notes without even being asked to log in.