You're right, I do feel dumb for trying it. It's just that it's the method I used last time I downgraded from the same system version (4.0), so I figured it'd work again.
Also, my Wii is a launch Wii.
The reason I restarted my Wii so many times was because I had previously gotten the same error message, and it would go away after several restarts. I didn't have hope, but I figured it was worth a shot.
I never installed BootMii because I didn't like the startup menu, and I didn't figure out until now that I could prevent the startup menu from appearing unless I need it.