What is the most likely issue Susan faces if her Kerberos tickets are not accepted, given her setup is properly configured?

If Susan's Kerberos tickets are not accepted despite her setup being properly configured, the most likely issue she faces is related to time synchronization. Kerberos relies heavily on accurate timekeeping between the client and the Key Distribution Center (KDC). Each ticket contains a timestamp, and both the client and server must agree on the same time to ensure the validity of those tickets.

If the client's time clock is unsynchronized with the KDC, the tickets generated by the KDC will be regarded as invalid by the client or vice versa. This is particularly critical in Kerberos, which has a built-in mechanism to prevent replay attacks, and therefore it allows only a small window for which tickets are valid. A common requirement is that the clocks on the client and server must be within a few minutes of each other, often set to five minutes. If they fall outside this range, authentication will fail.

While other issues such as server overload, strict password policies, or blocked network ports may lead to difficulties in accessing resources, they do not directly relate to the validity of the tickets in the context of time synchronization. Thus, an unsynchronized time clock stands out as the key issue when Kerberos tickets are being rejected.