Ensure that you placed the FNV4GB.exe file inside the exact same folder as the game's main executable. Do not run it from your Downloads folder or your desktop. "The game crashes immediately on startup after patching"
To clarify, there is for Fallout: New Vegas fnv 8gb patch fix
The implementation of the patch fix resulted in significant improvements to the stability and performance of FNV on systems with 8GB of RAM. Key findings include: Ensure that you placed the FNV4GB