dlu, thank you for the insightful explanation (there is a bug with version 4.6.3 installer that is cached by the Windows operating system. So when you try to upgrade to 4.6.4 the operating system grabs the 4.6.3 uninstaller that is cached and uses that to do the uninstall process. We don't have a way of forcing Windows to use the fixed 4.6.4 installer to do the uninstallation, so there doesn't seem to be anything we can do from within our application.) The problem reproduces with Windows 8 x64 and Office 2013 x64. If that is at all possible, I would rather clean the system from the exact files and registry entries based on information (or using scripts) provided by Evernote, than rely on general heuristics of 3rd party removal tool that may or may not clean all the remains of buggy Evernote 4.6.3 installer. I have another system with Windows 7 x64, Office 2013 x64 and Evernote 4.6.3 where the upgrade to 4.6.4 was not tried. What would be your recommendation, assuming that 3rd party removal tools are not used? Should a user wait for further instructions/KB article from Evernote (v. 4.6.3 itself is working fine)?