The NetServerHandler isn't supported anymore

We don't have any plans to update the plugin currently since we're not actively hosting a server or even using Bukkit... that being said there is a fork that was updated not to use NetServerHandler I believe... you can find that here: https://github.com/nightpool/Rejewled (it might need a little work but that mod author would be more in tune with what is necessary to get it up to date from his version)

I hope that helps :)