I've downloaded Super smash bros, then i installed usb loader. I do am able to play the game, but at the end of any fight in adventure mode i get the message "An error has occurred. Press the Eject Button, remove the Game Disc, and turn the power off. Please red the Wii Operations Manual for more information."
Maybe your USB device, if it's a hard drive, is spinning down. This is a typical issue with some hard drives. Sometimes you can use manufacturer software to change the setting if you need to.
Not really doing much Wii stuff these days.