No need to re-download RailWorks all over again.
It seems like you're experiencing a problem with the Steam-client or some settings.
Make sure you're running the Steam-Client and RailWorks executable files with Admin level privileges.
From the Steam-client Steam settings, try unchecking the following options:
From the "In Game" tab, un-check the "Enable Steam community in-game" option.
From the Downloads & Cloud option, un-check the "Enables Steam Cloud synchronization... " option.
From the Library, right-click on RailWorks, Properties, General-tab, un-check "Enable Steam-community in game" and the Updates tab select "Do not automatically update this game".
Then try going into Offline mode from the Steam-client.
If that still doesn't work, here's details about how to do a Clean Install of the Steam-client.
Follow the instructions there so you won't have to re-download your Games you got via Steam.
http://developer.valvesoftware.com/wiki ... ling_SteamIf that still doesn't work, then you might consider contacting Steam Support.
Good luck.