Introduction

Every website owner will eventually encounter an error. A page may suddenly show 404 Page Not Found, WordPress may display a Critical Error, a server may return 500 Internal Server Error, or a domain may stop resolving because of a DNS problem.

These errors can look complicated, but most of them provide an important clue about where the problem is located.

This complete guide explains the most common website, domain, DNS, SSL, hosting, server, PHP, database, and WordPress errors, what they mean, their common causes, and what you can check to resolve them.

Client Errors (400-499)

400 Bad Request

What it means: The server cannot properly process the request sent by the browser or application. The request may contain invalid information, malformed parameters, an incorrect URL structure, or data that the server does not understand.

How to fix it: Refresh the page first. Clear browser cookies and cache. If the problem continues, check the URL and application/server logs.

401 Unauthorized

What it means: Authentication is required before the requested resource can be accessed. You may see this error when accessing a protected directory, API, account area, or website resource without valid authentication.

How to fix it: Log in again and verify your credentials. For APIs or server applications, check authentication tokens and access credentials.

403 Forbidden

What it means: The server understood the request but refuses to allow access to the requested resource.

How to fix it: Check file permissions, directory permissions, .htaccess, security plugins, ModSecurity rules, firewall configuration, and server error logs. Do not simply disable security permanently. Identify which rule is causing the block.

404 Page Not Found

What it means: This is one of the most common website errors. It means the server cannot find the requested resource or URL.

How to fix it:

• Check the URL first.
• If using WordPress: Go to Settings → Permalinks and click Save Changes.
• Check .htaccess, rewrite rules, redirects, and whether the requested file or page actually exists.

SEO Note: Large numbers of unnecessary 404 URLs can create a poor user experience. If a page has permanently moved, consider using a 301 redirect instead of leaving users on a 404 page.

405 Method Not Allowed

What it means: The server understands the HTTP request method but does not allow that method for the requested resource.

Common causes: Incorrect API request • Server configuration • Application routing problem • Security rules • Incorrect HTTP method

408 Request Timeout

What it means: The server did not receive a complete request within the time it was prepared to wait.

Common causes: Slow network connection • Server overload • Proxy timeout • Application delay • Large or slow requests

429 Too Many Requests

What it means: The server or application is receiving too many requests from a client within a specific period.

How to fix it: If you are a website visitor, wait and try again later. If you manage the server, check rate limits, firewall rules, access logs, bot traffic, API limits, and application performance. Do not simply remove rate limiting if it is protecting your website from abuse.

Server Errors (500-599)

500 Internal Server Error

What it means: This is a generic server-side error. It means the server encountered an unexpected condition that prevented it from completing the request.

For WordPress: If WordPress suddenly shows a 500 error, check the most recent changes first:

• Recently installed or updated plugin
• Recently changed theme
• PHP version change
• .htaccess modification
• Server configuration change

Check the PHP and web server error logs to identify the actual cause.

502 Bad Gateway

What it means: A gateway or proxy server received an invalid response from an upstream server. This commonly happens when services such as a reverse proxy, CDN, load balancer, or web server cannot communicate correctly with the backend application.

How to troubleshoot: Check origin server status, PHP-FPM status, Nginx/Apache logs, server resource usage, firewall, reverse proxy configuration, and CDN configuration.

503 Service Unavailable

What it means: The server is temporarily unable to handle the request. Common reasons include maintenance or server overload.

For WordPress: WordPress may show a 503 error because of plugin problems, PHP resource limits, high traffic, hosting resource exhaustion, maintenance mode, or server-side service problems. Check server resource usage and logs.

504 Gateway Timeout

What it means: A gateway or proxy does not receive a timely response from the upstream server.

How to fix it: Investigate the slow component rather than simply increasing the timeout. Check PHP execution time, MySQL queries, server CPU/RAM, PHP-FPM, Nginx/Apache, CDN/proxy timeout, and external API response time.

DNS & Domain Errors

DNS_PROBE_FINISHED_NXDOMAIN

What it means: DNS could not find the requested domain name.

How to fix it: Check domain registration status, nameservers, DNS zone, A/AAAA records, CNAME records, and DNS propagation. If the domain has expired, renewing the domain may be necessary.

ERR_NAME_NOT_RESOLVED

What it means: The domain name could not be resolved to an IP address.

Common causes: DNS problem • Incorrect nameservers • Missing DNS record • Local DNS cache • Domain registration issue

How to troubleshoot: Try the domain from another network and check the DNS records. If it works on one network but not another, local DNS caching or resolver issues may be involved.

SSL & HTTPS Errors

NET::ERR_CERT_DATE_INVALID

What it means: The browser believes the SSL certificate is expired, not yet valid, or there is a problem with the system's date/time.

Common causes: Expired SSL certificate • Incorrect certificate validity dates • Incorrect server time • Incorrect certificate installation

How to fix it: Check the certificate's validity period and ensure the correct certificate is installed for the domain.

NET::ERR_CERT_COMMON_NAME_INVALID

What it means: The SSL certificate does not correctly match the hostname being accessed.

Common causes: Wrong SSL certificate • Missing www hostname • Incorrect virtual host • Incorrect CDN SSL configuration

WordPress Errors

WordPress Critical Error

What it means: "There has been a critical error on this website" usually indicates a serious PHP/application error prevented WordPress from completing the request.

How to troubleshoot: Start by identifying the most recent change. Check WordPress debug logs, PHP error logs, recently updated plugins, theme functions, PHP version, and memory limits. Do not immediately reinstall WordPress. First identify the actual PHP error.

Error Establishing a Database Connection

What it means: WordPress cannot establish a connection to its MySQL/MariaDB database.

How to fix it: Check the WordPress database configuration and verify that the database server is running. Also check database server logs and connection limits.

WordPress White Screen of Death

What it means: The website displays a completely blank page without the expected WordPress content.

Common causes: PHP fatal error • Plugin conflict • Theme conflict • Memory exhaustion • PHP compatibility issue

How to troubleshoot: Enable appropriate WordPress debugging/logging, inspect PHP error logs, and isolate recently changed plugins or themes.

WordPress 404 Error on Posts and Pages

What it means: Sometimes the WordPress homepage works while individual posts or pages return 404. A common cause is broken rewrite/permalink configuration.

How to fix it: Go to WordPress Dashboard → Settings → Permalinks and save the permalink settings again. Also check .htaccess and web server rewrite configuration.

PHP Errors

PHP Memory Limit Exhausted

What it means: The PHP process reached its configured memory limit.

How to fix it: Review the application's memory requirements and server configuration. Increasing memory may help, but it is also important to identify inefficient code or plugins causing excessive memory usage.

Maximum Execution Time Exceeded

What it means: A PHP script took longer than the configured maximum execution time.

Common causes: Large imports • Backup operations • Slow API requests • Heavy plugins • Slow database queries • Large file processing

Solution: Investigate why the operation is taking too long before simply increasing the timeout.

Server & Hosting Errors

Website Loading Very Slowly

Possible causes: Large images • Unoptimized JavaScript • Too many plugins • Slow database queries • High server load • Poor caching • External API delays • CDN configuration • Insufficient hosting resources

What to check: Check website performance, server CPU/RAM usage, database queries, PHP processes, caching, image optimization, and network latency.

MySQL Too Many Connections

What it means: The database server has reached its configured connection limit.

Common causes: High traffic • Poor application connection handling • Long-running queries • Insufficient database configuration • Multiple applications sharing the same database server

How to Troubleshoot Any Website Error

When a website stops working, do not immediately change multiple settings. Follow a structured process.

Step 1: Record the exact error

Write down the exact message and HTTP status code: 404, 403, 500, 502, 503, 504, DNS_PROBE_FINISHED_NXDOMAIN, SSL certificate error, WordPress Critical Error, etc.

Step 2: Determine the scope

Check whether the problem affects: One page • The entire website • WordPress admin only • One device • Everyone • One network • Multiple networks

Step 3: Check recent changes

Ask what changed immediately before the error appeared:

• Plugin update
• Theme update
• PHP update
• DNS change
• Nameserver change
• SSL change
• Server migration
• .htaccess change
• New firewall rule

Step 4: Check DNS

Verify A record, AAAA record, CNAME, nameservers, DNS propagation, and domain status.

Step 5: Check SSL

Verify certificate validity, hostnames, HTTPS configuration, redirects, and CDN SSL mode.

Step 6: Check server resources

Review CPU, RAM, disk space, PHP processes, MySQL connections, network, and server load.

Step 7: Check logs

Logs are often the most useful source of information. Check web server error logs, PHP error logs, WordPress debug logs, MySQL logs, firewall/security logs, and application logs.

Final Conclusion

Website errors are not random messages. Each error provides a clue about what is happening between the visitor, domain, DNS, network, server, application, and database.

• A 404 usually points toward a missing resource or route.
• A 403 indicates access is being refused.
• A 500 generally means an unexpected server/application failure.
• A 502 or 504 often involves communication or timeout problems.
• A 503 commonly indicates temporary unavailability or resource pressure.

For WordPress websites, plugins, themes, PHP, .htaccess, permalinks, databases, and hosting resources can all contribute to an error. The most effective approach is to identify the exact error, determine its scope, check recent changes, and then use logs and system information to locate the underlying cause.