1. Make sure Steam and Slender: The Arrival are closed completely (Steam can't be running in the background or this will not work)
2. Open "Registry Editor" in Windows
3. On the left, find HKEY_CURRENT_USER then find SOFTWARE then find BLUE ISLE STUDIOS then find SLENDER - THE ARRIVAL. Click on SLENDER - THE ARRIVAL
4. On the righthand side you will see a list of items. Find the ones that start with CB (examples: cb_00_h176621627 and cb_16_h176621532). Delete all 50 of these cb items out of the registry by highlighting them all, rightclicking, and selecting DELETE. It will give you a warning that this could cause system instability. Just select YES.
5. Launch the game from the icon in your system folders (again, if Steam is running this will not work so it's best to not use Steam at all to launch this game so that you don't have to worry about shutting down Steam after every single run).

You have to do this after every single run so that you can start with a fresh scrapbook. There might be other ways of doing it but this is how I've done it for years now.