I think that I figured it out. Do this: Download the latest patch to the game then launch it, it will say you have the latest version installed, ignore that. There is a drop down box that has the main game and the steel inferno DLC, click Steel Inferno DLC then in the box under it put in your seria...

Can you please elaborate how to do this? I have also bought Steel Inferno and have the same issue... My updater app is updated to latest version, but when I start it it just confirms the existing game is up to date and if I start Steel inferno installation, it requests I download the newest update a...