我发现问题的版本是 3.0.1在 /app/admin/ajax/weixin.php的第256行附近

 $account_info = array(
       'weixin_mp_token' => trim($_POST['weixin_mp_token']),
       'weixin_account_role' => $_POST['weixin_account_role'],
       'weixin_app_id' => trim($_POST['weixin_app_id']),
       'weixin_app_secret' => trim($_POST['weixin_app_secret'])
);

增加一行参数     'weixin_encoding_aes_key' => trim($_POST['weixin_encoding_aes_key']) 变成

 $account_info = array(
        'weixin_mp_token' => trim($_POST['weixin_mp_token']),
        'weixin_account_role' => $_POST['weixin_account_role'],
        'weixin_app_id' => trim($_POST['weixin_app_id']),
        'weixin_app_secret' => trim($_POST['weixin_app_secret']),
		'weixin_encoding_aes_key' => trim($_POST['weixin_encoding_aes_key'])
);

就可以了