Errors such as SEC_E_LOGON_DENIED can be annoying when executing Kerberos authentication in C++, particularly following a Windows upgrade. Changes in security rules or misconfigurations, including erroneous Service Principal Name (SPN) settings, are frequently the cause of this problem. Checking authentication logs, modifying permissions, and confirming client-server time synchronization can all help fix problems. Comprehending these elements guarantees more seamless authentication procedures, whether working on enterprise-level authentication or troubleshooting security protocols.