I wouldn't advise you to downgrade your wiis menu. That has been known to cause a full brick.
Updating the Wii has stubbed the CIOSes needed to run usb loaders. Use multi mod manager to unstub and remove them. If this fails then load IOS 36 then try again and it should work. However this is what works on my 4.3e, I'm assuming it would be the same for 4.3u.
Then follow the soft mod any Wii guide to reinstall the CIOSes to get the loader (s) working.