RoundCorner plugin error, "Corner at fault is highlighted...

[Sin4ddict]

Hello, I can't seem to round these corners:

It's a joist hanger, like this:

.skp file attached:
joist hanger.skp

I'm really not sure where I go wrong. Any help is appreciated!

[juju]

SketchUp isn't very good with small geometry. Scale it up 10x (or 100x or 1000x, whatever suits the situation), do the rounding you want, scale it back down by the same factor.