Hi everyone,
Earlier today there was a problem with InternetNZ which has resulted in several providers failing to resolve names ending in .ac.nz for their customers (apparently an issue while resigning the zone from what I heard). 
Some providers that we've contacted directly have been able to resolve the issue by either clearing the cache or restarting their recursive resolvers.
Could you please check whether your resolvers are affected and take appropriate action?
Thanks,
Diego