i have same issue after updating to ios249 rev19, but for me cfg loader runs and plays games fine. It's only wiiflow and usb loader gx that won't run. GX black screens and locks up wii right after running it from homebrew channel and wiiflow returns back to wii menu. I've been having a heck...
i also extracted IOS56 from the iso and installed it via wad manager but am still unable to get it to run from a USB Loader (using USB Loader GX updated to most recent release available from updating within gui)