Be sure to surround the paths with parenthesis if you aren't, like this:
Code:
java -jar NUSPacker.jar -in "C:\Users\DaddyBlair\Downloads\Video\Darts Up" -out "C:\Users\DaddyBlair\Downloads\general" -encryptKeyWith WIIU-COMMONKEY-HERE
If you are, and it still doesn't work, then try opening a command prompt in the directory containing your Darts Up folder, and then using relative paths instead of absolute paths. For example:
Code:
java -jar NUSPacker.jar -in "Darts Up" -out "Darts Up NUSpacked" -encryptKeyWith WIIU-COMMONKEY-HERE
If it still fails, something may be wrong with your installation of Java. Try completely uninstalling Java and reinstalling the latest version of the Java SE Runtime Environment.