Two workstations are connected to a LAN that does not have internet access.

Certificate security warnings commonly occur when a system cannot properly validate the validity period of an SSL/TLS certificate. According to CompTIA Core 1 (220-1201) networking and security fundamentals, two of the most common causes of certificate errors are expired certificates and incorrect system date and time.

After a power outage, systems without internet access cannot automatically synchronize time with an NTP server. If the system clock resets or becomes inaccurate, the browser may interpret a valid certificate as expired or not yet valid, triggering an “insecure site” warning. Setting the correct system date and time in the BIOS immediately resolves this mismatch and is a primary troubleshooting step.

Additionally, renewing the SSL certificate resolves errors if the certificate has legitimately expired or was invalid at the time of access. This is especially relevant for internal network services using self-signed or internally managed certificates.

Replacing the CMOS battery can prevent future time resets but does not immediately correct the certificate error. Adjusting browser security settings is unsafe and not recommended. Firewall port configuration and network scanning are unrelated to certificate validation.

CompTIA emphasizes validating time/date accuracy and certificate status as core steps when resolving certificate-related security warnings.