Admission / Admission Settings / Online Reregistration / Online Reregistration Notifications & Messages / Re-registration non-Eligible message
Here you can write a free text as message you want to show to end users that are not eligible for re-registration.
Note that non-eligibility is based on annual results, so “Enable Re-registrations based on Annual Results” setting in Admission / Admission Settings / Online Reregistration / Basic Settings, must be active.