Have you opened the ISO in WiiScrubber to see if the version you downloaded has the update partition removed?
I've had RegionFrii corrupt a few ISOs before, not allowing them to be brickblocked before. I can't remember, but I think that an error message might occurr if the ISO is already brickblocked, and you try to run it again. I always keep the .rar files (if the ISO is archived) so if I mess up the ISO, I can extract it again, and delete everything when I confirm it working. You could try brickblocking it first, and then use RegionFrii to change the region.