Yeah, it takes a bit to get the hang of it, but once you, you'll be fine.
Did you restart the computer afterwards to apply?
I noticed that you have the .ico file on your desktop. I would recommend keeping it saved in one of your C:\Users\Public
folders instead to avoid access issues with any other user account since the Public folders can be accessed by all users by default. Afterwards, you could just mofify the registry for the new path.
If the above doesn't help, then please go ahead and ZIP the add.ico file, and upload it. I'll be happy to do some playing with it to help rule it out as a cause or not as well.