Wii U USB helper "index was outside the bounds of the array"

[GBAtemp]

Hi first time posting here, so forgive mw if i posted in the wrong place, I've been trying to download animal crossing gamecube using the wii u usb helper, i have the iso and the download goes fine until the second step where it tells me "error: Index was outside the bounds of the array" I've been searching for a solution/what it means, but have found nothing, i'm probably just being an idiot but i could use some help, i'm pretty new to wii u stuff

Source: https://gbatemp.net/threads/wii-u-usb-h ... ay.645508/