That looks like it was the problem. Oddly, it seems like I must be logged in with admin privs before I can run NISpy on this machine. Even if I install as admin, I can't run it as a regular user (I don't get any error this time, but the .spy file shows up as blank).
If I log back in with admin privs, then everything works fine.
Dunno where the problem lies, but in any case I have a way to make this work. Thanks!