I can’t help you with the installer as I have never used it. However, I would suggest that you install scenarios in the old fashioned way.
1. Get a copy of 7 zip (it’s free) – https://www.7-zip.org/
2. Then unzip the downloaded scenario file to the desktop – the file name will be the same as the downloaded zip. The directory inside should be called “content”.
3. Open you Railworks directory – …. \Steam\steamapps\common\RailWorks, and move the content file there.
4. You should now have the scenario when you start the game.
Tim
