请教8老师和网友

我父母是分开办的移民，母亲已经在美国，130/485 同时递交。父亲在国内，130 已经批准，目前在 National Visa Center 递交文件。我在为我父亲提交DS-260后， 收到网上签证中心的message as following " The petition you have filed does not allow derivative status for family memebers. This means that any spouse, unmarried child under age 21, or parent will require his or her own petition to immigrate".

请帮忙解惑。多谢。