SSL (Secure Sockets Layer), or more accurately TLS (Transport Layer Security), keeps your site secure by enabling encrypted communication and authenticated connections through digital certificates. It encrypts data moving between a browser and a website. When someone visits your website, SSL/TLS ensures the connection is fully encrypted and verifies the authenticity of your site. It also protects the integrity of data against interception or tampering.
This is why browsers show a padlock. It is not just a symbol. It is the browser telling the user, “This connection looks safe.”
What happens when SSL goes wrong
When an SSL error appears, the browser responds with a warning. It shows a full-screen warning. Users see messages like “Your connection is not private” or “This site is not secure.” Many leave immediately. Some never come back.
In this article, we will go through the most common SSL certificate errors, explain why they occur, and show how to fix them step by step. This will help your organization stay secure and avoid major failures in the future.
8 Common SSL Certificate Errors and How to Fix Them
1. SSL Certificate Not Trusted
This is one of the most common and most alarming errors users see.
What it means
The browser does not trust the certificate presented by the website. From the browser’s perspective, it cannot confirm who issued it or whether it should be trusted.
How this shows up in real life
A developer installs a self-signed certificate for testing and forgets to replace it. The site goes live. Visitors open the page and immediately see a warning saying the connection is not private.
Why it happens
- The certificate is self-signed
- Intermediate certificates are missing
- The issuing Certificate Authority is not trusted by the browser
How to fix it
This error can be fixed by using a certificate from a trusted Certificate Authority. The certificate should be installed correctly on the server. It’s important to have the full certificate chain in place so browsers can trace trust all the way to a recognized root. Checking everything before going live usually stops this error from appearing.
2. Certificate Name Mismatch
This error looks technical, but the reason is very simple.
What it means
The domain name in the browser does not match the domain names listed in the certificate. Browsers always compare the website address with the Common Name and SAN entries inside the certificate.
Example
A user visits www.comsigntrust.com, but the certificate only covers comsigntrust.com. The browser rejects it and shows ERR_CERT_COMMON_NAME_INVALID.
Why it happens
- The certificate does not include all required domains
- Missing www, subdomains, or alternative domain names
How to fix it
The solution is making sure the certificate actually matches how users access the site. Every domain, subdomain, and variation needs to be included when the certificate is issued. Planning domain coverage upfront avoids last-minute reissues and browser warnings.
3. Expired SSL Certificate
This one is simple and still surprisingly common.
What it means
SSL certificates have an expiration date. Once that date passes, browsers treat it as an invalid SSL certificate, immediately warning users that the site is not secure. This common mistake is why automated SSL certificate management is so important: it removes the risk of human error and ensures renewals happen on time.
Why it happens
- The certificate was not renewed on time
- No monitoring or alerting was in place
How to fix it
This happens when renewals are treated as a reminder instead of a system. Central tracking and automatic renewals ensure certificates never expire silently. When renewals are tested early, outages stop being a risk altogether.
4. Incomplete or Incorrect Certificate Chain
This error often confuses teams because the certificate itself looks valid.
What it means
The browser cannot build a full trust path from the site certificate to a trusted root Certificate Authority.
Why it happens
- Intermediate certificates were not installed on the server
- Server configuration is incomplete
How to fix it
Even a valid certificate fails if the browser cannot verify the full trust path. Installing the complete chain provided by the Certificate Authority allows browsers to validate the connection instantly. This is usually a configuration fix, not a certificate problem.
5. Mixed Content Errors
This error breaks the padlock without fully blocking the site.
What it means
The page loads over HTTPS, but some resources load over HTTP. This weakens the security of the page.
Why it happens
- Hard-coded HTTP links in code
- Third-party scripts or assets loaded insecurely
How to fix it
Mixed content disappears once every resource loads securely. When images, scripts, and stylesheets follow the same HTTPS standard as the page itself, the connection remains fully trusted. Regular scans help catch insecure assets before users notice.
6. Certificate Revoked or Blacklisted
This error is serious and should never be ignored.
What it means
The Certificate Authority has revoked the certificate. Browsers check revocation status using OCSP or Certificate Revocation Lists (CRLs) and may refuse the connection if the certificate is revoked.
Why it happens
- The private key was compromised
- The certificate was misissued
- Security policy violation detected by the CA
How to fix it
Once a certificate is revoked, it cannot be reused. The only safe response is to issue a new certificate with a fresh private key and review how the original was handled. Strong key management prevents this situation from repeating.
7. Outdated Encryption or Protocol Errors
This is where old infrastructure shows its age.
What it means
The server only supports outdated protocols or weak encryption. Modern browsers refuse to connect.
Why it happens
- Old TLS versions are still enabled
- Outdated server software
How to fix it
Modern browsers expect modern security standards. Updating server configurations to support current TLS versions and disabling outdated protocols restores compatibility.
- Enable TLS 1.2 and TLS 1.3
- Disable old SSL and TLS versions
- Keep servers and libraries updated
8. ERR_SSL_PROTOCOL_ERROR
This error feels vague, and that is because it is.
What it means
The SSL handshake between the browser and server failed. The cause can be on either side.
Why it happens
- Incorrect server TLS configuration
- Browser cache issues
- Firewall or antivirus interference
How to fix it
This error clears once the handshake between the browser and server is properly aligned. In many cases, it comes down to outdated local data, security software interference, or misconfigured TLS settings. A clean environment on both ends usually resolves it quickly.
User-Side Browser Fixes
Most SSL errors look serious, but they are usually caused by simple system mismatches or outdated data.
Fix the basics first, such as time, cache, and dependencies. This resolves the majority of issues without touching the server.
1. Sync Your System Date and Time
SSL certificates rely heavily on accurate time settings. If your device’s date or timezone doesn’t match your browser, certificate validation can fail instantly.
On macOS:
Go to System Settings → General → Date & Time and enable Set date and time automatically.
On Windows:
Open Settings → Time & Language → Date & Time.
Make sure Set time automatically and Set time zone automatically are both enabled.
This one fix alone resolves a surprising number of SSL errors.
2. Clear Your Browser Cache
Old or corrupted cache files can interfere with SSL handshakes, especially when certificates have been updated on a website.
Google Chrome:
Click the three dots → Settings → Privacy & Security → Clear browsing data
Select Cached images and files, click Clear data, then restart Chrome.
Firefox:
Go to Settings → Privacy & Security
Scroll to Cookies and Site Data, click Clear Data, check Cached Web Content, and confirm.
Safari (Mac):
Click Safari in the top menu → Clear History
Choose a time range and confirm.
Clearing cache removes outdated SSL data and often fixes the issue instantly.
3. Keep Your Libraries and Dependencies Updated
If you’re working with custom scripts or scraping tools, outdated libraries can trigger SSL errors even when the website is fine.
Make sure:
- SSL-related libraries are up to date
- Frameworks and runtimes are running supported versions
Outdated dependencies are a silent cause of failed secure connections.
4. Avoid Websites with Expired SSL Certificates
Some SSL errors aren’t on your side. If a website is using an expired or misconfigured certificate, there’s no clean workaround.
If you’re unsure:
- Check the certificate details in the browser
- Report the issue to the site owner
For scraping projects, it’s best to avoid unstable or poorly maintained sites altogether.
5. Clear SSL State on Windows
On Windows systems, cached or corrupted certificates can cause repeated SSL failures.
To clear them:
- Open Control Panel
- Go to Network and Internet → Internet Options
- Open the Content tab
- Click Clear SSL State
- Confirm and restart your browser
This removes old certificate data and resets secure connections.
Trust Partners and SSL Management
By now, one thing should be clear. Most SSL errors are not mysterious. They are predictable, preventable, and often caused by a lack of visibility or ownership.
We at Comsigntrust are a recognized authority in SSL and digital trust. We provide certificates that browsers and enterprise systems widely trust. More importantly, we focus on proper deployment and ongoing management, not just issuing certificates.
FAQs:
What are the most common SSL certificate errors?
The most common SSL certificate errors usually come down to trust, timing, or configuration. These include certificates that are not trusted by the browser, expired certificates, hostname mismatches, missing intermediate certificates, mixed content issues, and servers using outdated encryption protocols. Each of these stops the browser from verifying a secure connection. That is why users often see warning pages instead of your site.
Why do SSL certificate errors occur?
SSL errors rarely happen because the technology is complicated. They happen because certificates are treated as one-time installs instead of ongoing assets. Missed renewals, incomplete certificate chains, domain changes, outdated server settings, or lack of monitoring are the real causes. When ownership is unclear, small gaps turn into visible failures.
How can expired SSL certificates be fixed?
To fix an expired SSL certificate, renew or reissue it and install the updated version correctly on the server. The better approach is to prevent expiration before it happens. Using central tracking and automated renewals removes the risk and stops outages at critical moments.
What does an SSL hostname mismatch error mean?
A hostname mismatch means the certificate does not match the domain the user is trying to access. The browser checks the site address against the certificate’s listed domain names and rejects the connection if they don’t align. This usually happens when www, subdomains, or additional domains were not included during certificate issuance.
How can organizations prevent SSL certificate errors in the future?
Preventing SSL errors comes down to taking real ownership of them. Using SSL certificate renewal automation ensures certificates are tracked, validated, and renewed automatically, reducing risk and keeping user trust intact. Add clear processes, proper checks before anything goes live, and regular configuration reviews, and SSL stops being a constant risk. It becomes something you can actually rely on.
