FSOpenFile errors typically occur when the file in question could not be found. You said that you have all the files, but are they in the right place?
Specifically, if you are trying to open the Homebrew Launcher, you need to have the executable file for it (homebrew_launcher.elf) placed on the SD card under "wiiu/apps/homebrew_launcher", so the full path would then be "wiiu/apps/homebrew_launcher/homebrew_launcher.elf".