I know that site.
I've been downloaded the railcraft folder from here but when I copy the .rar file in "serverfolder-->mods" and launch the start.bat this is the error message:
I can not understand what is wrong.
Forge is properly installed on the client Minecraft and server.
But if I insert railcraft in the mods folder of my clients find the objects in the inventory of the mod but when I try to use one I disconnect from the server.