The paper contains two figures and which need to be downloaded separately. (If you print the paper with the figures,they will look better printed at 600dpi.)
There are two proofs of the main theorem given in the paper. Unfortunately, one of them contains an error, pointed out by Stephan Endrass and Duco van Straten. A short correction will appear in J. Alg. Geom.; Fortunately the second proof is correct.