EAP-TLS is a method of authentication that uses certificates to establish a secure tunnel between the client and the server3. The certificates have a validity period and must be renewed before they expire1. If the user has been on an extended leave and has not logged in to the computer in several months, it is possible that the certificate on the client or the server has expired and needs to be renewed2. The other options are not directly related to EAP-TLS authentication or 802.1X network access.