If you need to access files from system folders (like Program Files, Users\name\AppData etc.), then use environment variables.
If you just want to run a file from the current drive (for example E:\Games\MyGame\MyFile.exe), try it without the drive name:
"\Games\MyGame\MyFile.exe"
Or you can get the drive letter from the AppFolder expression: left(NWjs.AppFolder, 1)