I’ve recently been active on the R-help mailing list because I had some issues
with the default implementation of neural networks (nnet). Seems as if the
mailing list solved my problem or at least hinted me towards a solution. The
nnet function seems somewhat strict about its arguments.

http://www.mail-archive.com/r-help@r-project.org/msg118338.html
http://www.mail-archive.com/r-help@r-project.org/msg119643.html