To fix your RailWorks registry entry, please download and run this tool 

Run the tool and select 'RailWorks Registry Fix'  (Note: Windows 7 and Vista users should right-click the file and select 'Run as Administrator' to ensure this tool runs correctly)

Browse to the RailWorks.exe file, usually found in C:\Program

Double click on the .exe file to fix the registry entry

Once opened you will need to locate your railworks.exe file