Is probably the SD card wasn't read properly. The sd card slots on wii u is pretty bad, so maybe try blowing into it and reinserting it a few times until it works. If you need to check, Load the vwii menu and look at the bottom left, the sd card should be blue, if you can access it like normal, then it should be inserted properly, just try again.
Still I wonder why other people are telling you such other stuff you didn't ask, the first post was about "How can you control the homebrew loader without GAMEPAD" which i hope i answered. Someone really should have done something about that. Unless i missed the part when you asked for help on something else.