Hello,
Did you format in fat32 with this utility ==>
http://www.ridgecrop.demon.co.uk/index.htm?guiformat.htm
The best is with an external hard drive, as it is often said, the USB keys work poorly with the Wii.
Did you try to install your original games on your USB drive with USB LOADER GX ??
To try (I say try, not that it works):
Did you try to put your USB key in WBFS format, and see the result with usb loader gx or configurable loader v70 ??
By the same occasion, can you post a syscheck report, for control ??