求问中大选课的问题

林奈西UID：3542947

向各位善良好心的前辈们请教一个问题，是这样的，前几天收到研院发来的邮件 内容是这样的 Please be reminded that enrollment validation period begins from 10:00am on 22 July 2014 (Tuesday) and ends at 5:30pm on 25 July 2014 (Friday). During the enrollment validation period, you may login MyCUHK Portal at http://portal.cuhk.edu.hk/ to validate classes in the shopping cart to check time clashes, fulfillment of requisites, and term study load, etc.
这个enrollment validation到底需要不需要选课啊  因为我把该选的课放进shopping cart之后系统显示 you do not have a valid enrollment appointment at this time 请问这个到底是什么意思啊？？