Recently I have become interested in Nvidia’s work in the Physics aspect of game development. Once I found out about Flex being used in UE4, I knew I needed to try it. But I ran into a problem with it… While building the files in Visual Studio It came up with 7 errors claiming that certain files are corrupt and that it failed to produce items, I have been trying to download this for the past 2 hours give or take, and I didn’t want to completely redo the building step. The errors- Error 1 error CVT1107: ‘C:\Users\Charlie\Downloads\UnrealEngine-FleX\Engine\Intermediate\Build\Win64\UE4Editor\Development\Renderer\Module.Renderer.1_of_7.cpp.obj’ is corrupt
Error 2 error LNK1123: failure during conversion to COFF: file invalid or corrupt
Error 3 error : Failed to produce item: C:\Users\Charlie\Downloads\UnrealEngine-FleX\Engine\Binaries\Win64\UE4Editor-Renderer.dll
Error 4 error MSB3073: The command “…\Build\BatchFiles\Build.bat UE4Editor Win64 Development” exited with code -1.
5 IntelliSense: identifier “UNiagaraScript” is undefined
6 IntelliSense: this operator is not allowed in a constant expression
7 IntelliSense: the size of an array must be greater than zero
Cheers 
I have Just fixed the error by going to the directory and deleting the corrupted files, when the build resumes, It just replaces the files! hope this helps anyone who came here for an answer! 
Ok, Now I have More Problems… 
Every time I try to launch the project it crashes, No crash report, No error message, Nothing. If anyone can help it would be much appriciated
You haven’t given enough information for anyone to really help you. If you’ve built the engine (And since you are using the NVIDIA branch, we can safetly assume you are). Then make sure to run with a debugger, this will tell you where its crashing, and hopefully spit out some kind of error message. Alternate to this, you can check the log files.
Lastly try to explain where in the process it crashes. ie. At 45% may indicate a potential shader compilation issue.