I'm guessing the other errors are also due to incorrect folder arrangement.
yeah, for instance.. all those fredoscale files are supposed to be inside a folder called FREDOSCALE_Dir_20..
not sure what you have going with that folder "Curviloft 1.0c and LibFredo6 3.5c "
some of the TOS files are out of their folder as well.. (FreehandOnSurface.rb for instance should be inside the TOS folder..
that's after a quick glance and i'm sure there's plenty more..
it's looking like emptying the whole plugins folder and redownloading the plugins while following install instructions should do the trick