Looks like you're missing some CIOS.
If not, try with a version called: Configurable USB Loader.
If that doesn't work, check for any missing CIOS.
On a side note, not all the USB's works properly, and only the Wii's lower USB port works for this purpose.
EDIT: Please forgive my ignorance, I second read your post.
Then, try to use a different (lower) version of USB Loader GX.