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Troubleshooting Common Classic Editor Issues: 404, 403, and Update Errors

25 threads Sep 7, 2025 Plugin → Classic editor

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Many WordPress users rely on the Classic Editor plugin to maintain a familiar writing experience. However, conflicts with other plugins, themes, or server configurations can sometimes lead to frustrating errors that prevent you from saving or publishing content. This guide outlines the most common issues reported by the community and provides step-by-step solutions to resolve them.

Common Classic Editor Problems and Their Solutions

1. 404 or "Page Not Found" Errors on Save/Update

Problem: Clicking the "Update" or "Publish" button redirects you to a 404 error page instead of saving your changes.

Why it happens: This is often related to permalink structure conflicts or server-level redirect rules being triggered by the save process.

Solutions:

  • Refresh Your Permalinks: This is the most common fix. Simply navigate to Settings > Permalinks in your WordPress admin and click "Save Changes" without making any modifications. This action regenerates your site's rewrite rules.
  • Check with Your Hosting Provider: As seen in the threads, issues with ModSecurity or other server-level firewall rules (like Sucuri) can block the POST request to post.php, causing a 404 or 403 error. Contact your host's support and ask them to check the server error logs for ModSecurity rule triggers related to admin-ajax.php or post.php.

2. 403 "Forbidden" Errors on Save/Update

Problem: You receive a "403 Forbidden" error message when attempting to save a post or page.

Why it happens: This is almost always a server security measure. ModSecurity or similar Web Application Firewalls (WAF) may incorrectly flag the content you're trying to save as malicious, blocking the request.

Solutions:

  • Contact Your Hosting Provider: Provide them with the exact error from your server logs. They can identify which specific ModSecurity rule is being triggered (e.g., a false positive on a magnet link or specific HTML) and whitelist it for your site.
  • Temporarily Disable Security Plugins: If you use a security plugin like Sucuri, try temporarily deactivating it to see if the issue resolves. If it does, you will need to adjust the plugin's settings or whitelist the action in its configuration.

3. JavaScript Console Errors (e.g., "Uncaught TypeError")

Problem: Buttons like "Add Category" don't work, and your browser's JavaScript console shows errors like "Uncaught TypeError: Cannot read property ‘responses’ of undefined" or "Assignment to constant variable."

Why it happens: These errors typically indicate a JavaScript conflict with another plugin or theme.

Solutions:

  • Identify the Conflict: Disable all other plugins and switch to a default WordPress theme (like Twenty Twenty-One). If the error disappears, reactivate your plugins one by one to find the culprit. Common conflicts have been reported with page builders, security plugins, and custom meta boxes.
  • Check for Updates: Ensure all your plugins, your theme, and WordPress itself are updated to their latest versions, as updates often include compatibility fixes.

4. Fatal PHP Errors (White Screen of Death)

Problem: The edit screen fails to load entirely, showing a blank white screen or a fatal error message mentioning an "undefined function" or "[] operator not supported for strings."

Why it happens: This usually occurs when there is a code incompatibility, often because your version of WordPress is too old for the current Classic Editor plugin, or because your theme has a bug.

Solutions:

  • Update WordPress: The error Call to undefined function use_block_editor_for_post_type() specifically means your WordPress core is outdated and missing functions that the plugin requires.
  • Enable WP_DEBUG: Add define( 'WP_DEBUG', true ); to your wp-config.php file to get a more detailed error message, which will point to the exact file and line number causing the problem. This often reveals an issue in your theme's code (like the betheme error mentioned in the threads).

General Troubleshooting Steps

If you are unsure of the exact cause, follow this general process:

  1. Health Check Plugin: Install the official Health Check & Troubleshooting plugin. Its "Troubleshooting Mode" allows you to deactivate plugins and switch themes only for your user session, preventing site downtime for your visitors while you diagnose the issue.
  2. Check Server Error Logs: The most definitive way to diagnose 403 or 500 errors is to look at your server's error logs. Your hosting provider can usually help you access these.
  3. Clear Caches: Clear any caching from your site, including server-level cache, plugin-based cache, and your browser cache.

By methodically working through these steps, you can identify and resolve the conflict preventing the Classic Editor from working correctly, allowing you to return to a smooth content editing workflow.

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