I had the same problem a few months back; and Arthur Dalton showed me how to test the neutral safety swithc from the emgine compartment. Open the link following this paragraph, and scroll to the 4th post on the 2nd page. My engine started when I applied battery voltage to the switch as directed by Arthur, thus my NSS was at fault. Had a new one installed and the problem was solved.

http://www.peachparts.com/shopforum/showthread.php?t=108425&highlight=neutral+safety+switch

regards,
Mark