1. Backup Your Website

Before making any changes, ensure you have a full backup of your website files and database.

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2. Check the .htaccess File

The .htaccess file could be corrupted.

Steps:

1. Access your website files via FTP or File Manager in your hosting control panel.
2. Locate the .htaccess file in the root directory (where wp-content, wp-admin, and wp-includes folders are located).
3. Rename the .htaccess file to .htaccess_backup.
4. Check your website. If it works, go to the WordPress Dashboard → Settings → Permalinks, and click Save Changes to regenerate the .htaccess file.

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3. Increase PHP Memory Limit

The error may occur due to insufficient PHP memory.

Steps:

1. Edit the wp-config.php file.
2. Add the following line before /* That's all, stop editing! Happy blogging. */:
   php

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   define( 'WP_MEMORY_LIMIT', '256M' );

3. Save the file and check your website.

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4. Deactivate Plugins

A faulty plugin can trigger the error.

Steps:

1. Access the wp-content folder via FTP or File Manager.
2. Rename the plugins folder to something like plugins_backup.
3. Check your website. If it works, rename the folder back to plugins and activate each plugin one by one from the WordPress dashboard to identify the culprit.

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5. Switch to a Default Theme

A corrupted or incompatible theme might cause the error.

Steps:

1. Access the wp-content/themes folder.
2. Rename your current theme’s folder (e.g., yourtheme_backup).
3. This forces WordPress to default to a built-in theme like Twenty Twenty-Three.
4. Check your website.

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6. Check File Permissions

Incorrect file permissions can lead to this error.

Correct Permissions:

• Folders: 755
• Files: 644

Steps:

1. Use FTP or File Manager.
2. Ensure the permissions of your files and folders match the above values.

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7. Enable Debugging

Enabling debugging in WordPress may reveal the root cause.

Steps:

1. Open the wp-config.php file.
2. Find this line:
   php

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   define( 'WP_DEBUG', false );

3. Change it to:
   php

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   define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

4. Access your website again and check the debug.log file in the wp-content directory for errors.

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8. Reinstall Core WordPress Files

Core WordPress files may have become corrupted.

Steps:

1. Download the latest version of WordPress from wordpress.org.
2. Extract the ZIP file on your computer.
3. Upload the wp-admin and wp-includes folders to your site, overwriting the existing ones.

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9. Contact Your Hosting Provider

If the issue persists, it could be a server-level problem. Reach out to your hosting provider for assistance—they may be able to identify server errors or misconfigurations.