Hi! I don't know if this has been posted before, but I ran into an asset problem, and found a solution.
Several simmers have posted that they could not get assets to show up in RW. I just had this problem, and when I looked at the RW file tree, I found I had 2 asset folders. Railworks/Assets/Assets/Britkits, etc. When I copied the assets in the 2nd fold back into the 1st folder, my assets appeared in RW. It might be worth a try for people to check for duplicate folders within RW.