父母2000悲剧太痛苦了，帮忙找找原因吧（附英文邀请信）

情况是这样的，说起来都让我揪心。
我是结婚绿卡，老公是公民，本人现在上海，陪同父母，顺便给他们训练签证。爸爸上班，妈妈退休。
5/8号1000的时候，父母也不怎么紧张，签证官中年亚裔女，前面的给据了。
父母开始还怕怕的，结果几个问题就顺利通过了，回到家，收到护照，夹白条拒签。
vo问父母去干吗？父母答旅游。去多久：一个月。女儿绿卡看看，然后敲几个字，说好了。父母高兴出来。我给他们定了机票。
几天后悲剧了，夹了白条拒签。只能马上再约。约了5/19.
父母2000紧张了，签证前都睡不好，反复练习，再加上论坛上的取经，我让他们主动点。
vo中年白人男子，母亲上去，递了护照就说，是受我老公的邀请，由女儿陪同去玩，因为他们不会英语。vo点头。问出国国没有，妈妈回答没有。事实上爸爸护照上有泰国，越南，柬埔寨的签证，但是妈妈回答了，爸爸也没有更正，估计都紧张了。vo问去多久，妈妈说一个月，爸爸说还有爷爷奶奶要照顾，还要回来上班。签证官说不能给他们通过，爸爸笑着说，我们只是想去玩玩，什么原因不让我们通过。vo红了脸，结结巴巴说这个邀请信不能通过。
回来的路上，爸爸妈妈都很难过，也很不高兴，我也是找不到原因，邀请信我也附上，请大家看看，到底是什么原因了？
这个邀请信因为悲剧过，所以特别指出约束力，写的很诚恳，到底是什么原因了。
如果需要再签，应该是什么时候再去？请各位指点一二吧，谢谢啦。
Honorable Consular officer:

My name is ***, I’m writing this letter to invite my parents in law ***(passport #: ***) and ***(passport #: ***) for a temporary visit. We will take them to short trips which include New York, Boston, Philadelphia, and Las Vegas, mean while they will live with us in our apartment located in ***, New York. They will support their travel fees partially, and the money in my bank account will cover any other expense during this trip. Please find our financial proofs in the supporting material for visa application if needed.
I’m the citizen of United States, and I have worked for *** as software engineer for 7 years. I immigrated to United States with my family when I was young. I met my wife in 2009, and we got married in 2010. We don’t have child.
My wife *** is in Shanghai with her parents right now. She would like to bring her parents together with her as they can’t speak any English at all, we are worried them to fly and go through customs by themselves. She goes back to Shanghai every year for visiting her parents, grandparents, relatives and friends. We held a formal wedding in Shanghai last year, and I had a great time in Shanghai. My parents in law are very kind and friendly, and so I would like to be the host this year.
I’m sure that *** and ***will return to China on ***, 2014, I bought them round trip flight tickets as well. They have family ties, social links and financial backing to support this claim. First of all, my parents in law have two properties in Shanghai, one is primary home and another one is for renting. They need collect rent for every three months. Secondly, they have parents who are over 80 years old, which is my wife’s grandparents, they have to come back to take care of them. In addition, my father in law isn’t retire yet, he need come back to work as well. Last but not least, they have a lot of social links in Shanghai. For example: my father in law likes play Mahjong, he plays Mahjong with neighbors and friends almost everyday. My mother in law likes singing, she joined a singing group in ***, and she goes there every weekend. Also, they have a lovely dog live with them. They were born in Shanghai and have been lived in Shanghai more then 50 years; they have a stable life in Shanghai and enjoy it. So I believe that they have very strong tie which will compel them to return to China after their visit to the United States.
Your favorable consideration regarding their visa applications will be highly appreciated. If you have any questions regarding this latter, please kindly contact me or my wife at the address and telephone number below.
For your information, I have included the following information about us:

Name: ***Passport No: ***Date of Birth: ***Address: ***Telephone: ***E-Mail: ***
Name: ***Passport No: ***Date of Birth: ***Address: ***Telephone: ***E-Mail: ***
Sincerely Regards,
***
***
补充说明下，我在二千等父母出来的时候，遇到一个女孩情况和我一样，也是移民了，父母1000通过后，拿到护照拒签，然后父母来2000，但是她的父母签过了。