発見した。日本語でおｋ
1. Exit steam all the way
2. Navigate to your Steamapps folder under the Steam directory
3. You should have 5 or so .ncf cache files relating to rainbow six 2 in here, as well as a folder called "Common" under which rainbow six vegas 2 is installed
4. Since vegas 2 was the only game in Common for me, I simply renamed Common to Common2.
5. Start steam back up. It will create a new Common folder, a blank vegas 2 directory with some empty folders and an empty text file. The important part is that steam should now change status of the game from 0% or 100% to finished and ready to launch
6. Rename your old Common folder back (you can rename the new one, or proably delete it. I kept it just in case)
