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Resolving Common 'Mailchimp for WooCommerce' Database and Fatal Errors

69 threads Sep 7, 2025 Plugin → Mailchimp for woocommerce

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Users of the 'Mailchimp for WooCommerce' plugin often encounter a specific set of errors that can disrupt their site's functionality, from breaking the shopping cart to causing full site crashes. This guide compiles the most frequent issues and their solutions, based on community reports and resolutions.

Common Error 1: Database 'Duplicate Entry' Errors

Problem: The most common error is a WordPress database error: Duplicate entry '[email protected]' for key 'PRIMARY'. This occurs when the plugin tries to insert a cart record into the wp_mailchimp_carts table for an email address that already has an entry.

Why it happens: This is typically a race condition where multiple simultaneous AJAX requests from a user's browser try to update their cart at the same time.

Solution: This error is often just a notice and may not affect functionality. However, if it's causing issues, a standard first step is to perform a fresh reinstall of the plugin:

  1. Deactivate and delete the plugin from your WordPress admin.
  2. Go to your Mailchimp account dashboard and ensure your store is disconnected from the Connected Sites area.
  3. Install the latest version of the plugin directly from the WordPress plugin repository.
  4. Reconnect and reconfigure your settings.
This process ensures all database tables are created cleanly and can resolve the conflict.

Common Error 2: Fatal Errors and Site Crashes on Activation/Update

Problem: Users report fatal errors, such as Class 'MailChimp_WooCommerce_Rest_Api' not found or Call to undefined function mb_strpos(), which can make the site's backend inaccessible.

Why it happens: These are usually caused by one of three things:

  • Incomplete Update: The plugin files were not fully updated during the process, leading to missing classes or functions.
  • Outdated PHP: The plugin requires PHP functions (like mb_strpos) that are not enabled on older PHP versions (e.g., PHP 5.6).
  • Code Conflicts: A specific code conflict, such as when WooCommerce Admin is disabled via a filter.

Solution:

  1. Check PHP Version: Ensure your server is running a supported, modern version of PHP (7.4 or higher is strongly recommended). You can check this in your hosting control panel.
  2. Manual Reinstallation: If your site is crashed, use FTP or your host's file manager to rename the plugin folder (wp-content/plugins/mailchimp-for-woocommerce to mailchimp-for-woocommerce_OFF). This will deactivate the plugin and restore site access. Then, install a fresh copy.
  3. Review Code Filters: If you use a filter to disable WooCommerce Admin (add_filter( 'woocommerce_admin_disabled', '__return_true' );), be aware this has caused conflicts. The 'Mailchimp for WooCommerce' team has addressed this in newer versions, so updating may resolve it.

Common Error 3: Action Scheduler Table Errors

Problem: Errors stating that Action Scheduler tables don't exist, such as Table 'wp_actionscheduler_actions' doesn't exist. This can prevent the plugin from syncing data and sometimes break the cart.

Why it happens: The plugin uses a library called Action Scheduler to handle background tasks. If these database tables are not created correctly during installation, this error occurs.

Solution: A complete uninstall and reinstall, as described in the first solution, is the most reliable fix. This process should trigger the proper creation of all necessary database tables.

Common Error 4: High Server Load from API Requests

Problem: The plugin makes constant requests to /wp-json/mailchimp-for-woocommerce/v1/queue/work, causing high CPU usage and potentially crashing the database server.

Why it happens: This endpoint processes the background sync queue. If it gets stuck or there is a problem with the site's WP-CRON system, it can loop excessively.

Solution:

  1. Confirm that WP-CRON is functioning correctly on your host. Some hosts require you to enable it or set up a server-level cron job to trigger wp-cron.php.
  2. If the problem is acute, a plugin reinstall can help reset the queue process.

General Best Practices and Conclusion

Many persistent issues with the 'Mailchimp for WooCommerce' plugin can be resolved by ensuring a clean installation environment:

  • Use a supported PHP version (7.4+).
  • Keep WordPress, WooCommerce, and the plugin itself updated to the latest versions.
  • Perform a complete uninstall and reinstall as a first, crucial troubleshooting step.
Before taking any action, especially on a live site, it is always recommended to create a full backup of your website and database.

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