Games freezing during play while loading from a usb drive usually suggests that the drive is spinning down and going to sleep. It probably happens during parts of the game that require little to no disk reads, and to much time goes by and the drive spines down. Unfortunately the wii is unable to spin the drive up and the game crashes. If it is a portable drive there is usually a utility provided by the manufacture that will adjust the spin down settings. For the wii having the spin-down disable is usually best, or you can experiment with a higher time limit. You can test this by installing a problematic game to a usb thumb drive and testing it. Since usb flash drives don't spin down the game should play flawlessly if spin-down is your issue.