When a student is dropped from a session/class, from the roster in the ILT module in PASS, they are unable to sign up for the same session again and will receive this message when trying to register for it from their learning in PromisePoint:The student will have to be re-enrolled in the session/class's roster by an ILT PASS administrator. 

Instead of dropping a student from a session/class and to allow the student to re-enroll, the student should be marked as un-enrolled in the session's roster instead of dropped.

Dropping a student from a session/class is designed to force them to register for a different session then the one they were originally enrolled in. This could be because they chose the wrong session/class they were supposed to enroll in, and dropping them will keep them from re-enrolling in that specific session/class.