Error occurred when trying to make a draft release notes PDF

[Tiansworld]

Hi guys,
I was trying to make a draft release notes PDF by using the command:

"publican build --embedtoc --publish --formats pdf --langs zh-CN"

under my own translation git branch.

An error occurs and prevents publican from completing the job. The
error output is:

"Validation failed:
Cloud.xml:75: validity error : Element primary is not declared in
title list of possible children"

I checked xml file under en-US/Cloud.xml, but I don't know what to do.
I don't know xml.

The following steps were done before I did publican build
1. git pull git://git.fedorahosted.org/git/docs/release-notes.git master
2. tx pull -l zh_CN

How can I solve the error?