你好,我是读IT Diploma的新生,我在网上已经注册过课程了,我想看我的时间表,就在Virtual-Study里点Graphical Timetable,结果显示You are not registered in any classes for any current teaching periods.于是我返回点Register for classes,但却提示Class registrations for your course are currently unavailable.请问该怎么办?