How to Fix Common SSL Certificate Errors

SSL certificates are essential for securing websites, protecting user data, and building trust. Yet, even with a valid SSL installed, many websites struggle with one or more certificate-related errors. These issues not only disrupt the user experience but also affect SEO, website performance, and conversions.

In this guide, we break down the most common SSL certificate errors and provide clear, practical solutions for each. Whether you manage a single website or multiple domains, this step-by-step troubleshooting guide will help you diagnose and resolve issues quickly.

1. NET::ERR_CERT_DATE_INVALID

(Your connection is not private — certificate expired or not yet valid)

This is one of the most frequently seen SSL errors. It appears when the certificate is either expired, not active yet, or installed on a system with incorrect time settings.

2. “Your Connection Is Not Private” — Self-Signed Certificate Error

This appears when a website uses a self-signed SSL instead of a certificate issued by a trusted Certificate Authority. Browsers do not trust these certificates for public websites.

How to Fix It

• Replace the self-signed certificate with a trusted SSL from a recognized CA.
• For internal or staging servers, add the certificate to the trusted root store of your operating system/browser.

3. Mixed Content Error

(Your site is loaded on HTTPS but some resources still use HTTP)

Mixed content errors occur when images, scripts, or stylesheets are requested through HTTP while the page itself is served over HTTPS. This often breaks the green padlock indicator.

4. SSL Certificate Chain Issues

(“The certificate chain is incomplete” or “Intermediate certificate missing”)

Your SSL certificate must be installed with its intermediate certificates. Missing or incorrect chain files cause trust errors on mobile devices and older browsers.

How to Fix It

• Step 1 — Identify the missing intermediate: Use an online chain validator.
• Step 2 — Download the correct intermediate bundle: Get it from your CA’s official repository (e.g., DigiCert, Sectigo).
• Step 3 — Reinstall the certificate with the full chain:
  • On Apache: Use the SSLCertificateChainFile directive.
  • On NGINX: Append intermediates to your certificate bundle file.
  • On IIS: Import the chain into “Intermediate Certification Authorities”.

✔ Always verify after installation using an SSL checker tool.

5. Certificate Name Mismatch

Error: “The certificate does not match this domain.”

This happens when:

• The SSL certificate is issued for www.example.com but the website uses example.com.
• The domain is missing from the SAN (Subject Alternative Name) list.
• You are using a certificate on a different subdomain than intended.

How to Fix It

• Ensure the SSL is issued for every domain/subdomain you intend to use.
• Use a wildcard certificate if securing multiple subdomains (e.g., *.example.com).
• For multi-domain projects, purchase a SAN/UCC certificate.

6. Wildcard SSL Not Working on Sub-Subdomains

Wildcard certificates secure *.example.com (which works for blog.example.com, shop.example.com). However, they do not work for deeper levels like test.api.example.com.

How to Fix It

You need one of these options:

• A multi-level wildcard: *.api.example.com
• A SAN/UCC certificate listing all subdomains explicitly.
• A reissued wildcard certificate covering the correct level.

7. Browser Cache or HSTS Errors

Sometimes the SSL installation is correct, but browsers still show old warnings due to cached HSTS (HTTP Strict Transport Security) policies.

How to Fix It

• Step 1 — Clear browser cache and HSTS settings: In Chrome, go to chrome://net-internals/#hsts to delete domain security policies.
• Step 2 — Check your HSTS header: Ensure correct max-age and includeSubDomains settings are applied.

8. Server Misconfiguration or Multiple Certificates

On load balancers, proxies, cPanel/WHM, or IIS, more than one certificate may be bound to the same domain or IP address, causing conflicts.

How to Fix It

• Remove outdated or conflicting certificates.
• Ensure the correct certificate is bound to port 443.
• Restart the server after updating bindings.

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Final Checklist to Prevent SSL Issues Permanently

• ✔ Use a reputable Certificate Authority
• ✔ Enable HTTPS redirects site-wide
• ✔ Keep auto-renewal enabled (or set reminders)
• ✔ Regularly scan your SSL installation for errors
• ✔ Install full certificate chains correctly
• ✔ Keep server time synced with NTP
• ✔ Validate certificate SANs before issuing

Conclusion

SSL errors can affect your website’s trust, SEO performance, and credibility. The good news is that most issues can be resolved quickly with the right steps. By using proper certificate installation practices and monitoring tools like SSLCheckTools.com, website owners can eliminate errors and maintain a fully secure, high-performing website.