AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];

    manager.responseSerializer = [AFHTTPResponseSerializer serializer];//添加上这句即可  解决问题

ps:http://stackoverflow.com/questions/21620429/afnetworking-2-0-nslocalizeddescription-request-failed-unacceptable-content-ty

通过AF "get" 请求html页面总是失败的问题