When adding a Public Certificate to my GLP Server and setting a suitable Expiry Date, a User still shows an 'Inactive' - why is this?

Whilst it is possible to configure the Expiry Date of a Public Certificate within the GLP Server Configuration, the Public Certificate itself has an Internal Expiry Date. This Internal Expiry Date cannot be modified:
Once this date is passed, that Certificate will be invalid - a user will appear inactive if they do not have a valid in-date Public Certificate:
To resolve this issue, use your GLP Admin Account to request new certificates via the ADInstruments GLP Website.