The canonical website
http://cs.anu.edu.au/~bdm/nauty/
is misbehaving. It works for me but not for many other people.
We will track this down. Meanwhile, this version works:
http://users.cecs.anu.edu.au/~bdm/nauty/
and Adolfo's page in Rome also works:
http://pallini.di.uniroma1.it/
Brendan.