Actually 1.8.10 came out yesterday, not 1.8.7. Have you tried rebooting. It really does look like WFS is still open. You could also go into Task Manager → Details and kill it there.
Actually I just noticed you have the installer in the install folder. That folder gets wiped out by the installer. So if you are running the installer from the a folder it’s trying to delete, in essence, it’s trying to delete itself while its running. Move it to a different folder and you should be fine.