Joined this forum just to comment. Since moving to Win10 I (and others from this topic) have had problems getting F2F to work correctly.
Error message: "This file does not have a program associated with it for performing this action. Please install a program or, if one is already installed, create an association in the default programs control panel."
My windows installation was a Win7 upgrade, and I have also noticed that I have some other non-working context menus - such as "Register COM Server"
Other people have reported this problem but not really explained how the problem was resolved.
I tried the unregister shell program that you posted. If fact I believe that this is the same program, which is generated when the main program is "installed". In regedit I can see the context menu items added and removing correctly from the registry, with the correct CLSID. However, this does not solve the problem. The context menu shows the program item but does not "link" it to program.
I right-clicked on the Files2Folder.exe application itself and run the "Troubleshoot Compatibility" option. It suggested "Vista", requested that I try it out. It worked! Then save settings for compatibility.
Hope this is helpful for others.
BTW, Very useful and handy application, thank you for creating it.