
Do you have a modchip? it lets you play burned GC backup
if you don't have a mochip, did you installed a custom MIOS (cMIOS from Wiigator)? it lets you play burned GC backup without a modchip
Check this post :
http://gbatemp.net/threads/usb-loader-gx.149922/page-848#post-4628403

what did you "follow" ?
it's only a list of available method to play gamecube games on Wii/WiiU.
Which method did you choose?
What did you install, which loader, which version, etc.?