Again a clean and unatlered system? We assume your computer is not heavily overclocked and performing OK in other games and programs?
So the railworks.exe loads normally and when you press the "Start Train Simulator 2012" button the big black windows comes on for an instant before stalling with the error?
I haven't come across this error, but the message is about the C++ runtime libraries.
TS2012 installs some and Windows Update updates them once in a while.
I just had Windows Update do a 40 file 140 Megabytes update today, which included lots of the .Net framework things. TS2012 still started normally, but perhaps something on your computer got corrupted?
Only advice I can give you is not to do anything rash, retrace your steps and check the Windows Update for failed installs.
The C++ stuff that TS2012 needs can be re-installed from inside the Railworks folder. It shouldn't hurt to re-install the vcredist_x86.exe and physx...exe files from the Install folder inside your Railworks folder in the Steam/steamapps/common directory. These are core components of the RailworksProc2.exe progam that refuses to load. Windows should take care of the dotNet stuff itself so when there are no errors in the Windows Update history I see no need to re-install the dotNetFX40...exe, but it cannot hurt either.
Somebody else has more experience with these errors?