Error on new order email

This kind of problem may be caused by either a conflict with your theme or with another plugin.
 
The best way to determine this is to:
 

• Temporarily switch your theme to Storefront
• Disable all plugins except for WooCommerce
• Repeat the action that is causing the problem

If you’re not seeing the same problem after completing the conflict test, then you know the problem was with the plugins and/or theme you deactivated. To figure out which plugin is causing the problem, reactivate your other plugins one by one, testing after each, until you find the one causing conflict. You can find a more detailed explanation on how to do a conflict test here.

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Could you please enable WP_Debug on your site and let us know if you see any errors?

You can read more about how to enable WP_Debug here:
http://codex.ww.wp.xz.cn/Editing_wp-config.php#Debug

Here are the basic steps:

1. Login to your site through FTP
2. Make a backup of wp-config.php
3. Open this file and add the code below
4. Save and re-upload this file

Find this line of code: define('WP_DEBUG', false);

Change it be this:

// Enable WP_DEBUG mode
define('WP_DEBUG', true);

// Enable Debug logging to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);

// Disable display of errors and warnings 
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors',0);

Once you’ve done that, try making that error happen again. You will find a debug.log file created in your /wp-content/ folder – please send that to us so we can see what might be going on.

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Similar errors (but got fixed in the latest version of WordPress core):

* https://github.com/wp-cli/wp-cli/issues/3374
* https://core.trac.ww.wp.xz.cn/ticket/37736