Um, this not a real solution, but a possible workaround: if the output of the rails generate nifty:scaffold mymodel
command is still in your terminal buffer, you could manually delete the files it created.
And if the output isn't available, you could do rails generate nifty:scaffold mymodel2
in order to see what files nifty:scaffold created before manually deleting the corresponding files for mymodel
.
Not elegant, but it might get you over the hump.