Cornerstone editing not working : "The preview could not load due to the iframe ..."

Hello there :slight_smile:

Since yesterday is displayed this while I click on “edit with Cornerstone” : “The preview could not load due to the iframe response being incomplete. This is most often related to a plugin conflict, or customizations introducing a PHP error.”
Same with all others plugins turned off.

  • WP version is 4.9.1–fr_FR.
  • Cornerstone version is 2.1.7.

I saw a similar topic has been open last November, and closed today.
Is there anything we can do ?

Thanks for all !


Hello @Julien7,

Thanks for asking. :slight_smile:

This is most likely a memory issue. The following could help uncover more information:

  1. Enable WP_DEBUG and WP_DEBUG_LOG. You might be able to see an error message on the site right away. If not, the error log could reveal where the problem is originating.
  2. Try switching to parent theme in case child theme is being used on website to see if that makes a difference. The conflict could be in your customizations.
  3. Test for a plugin conflict.
  4. Try adding the code below in your wp-config.php file located at the root directory of your site.

define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );

You may add it before this line of code.

/* That's all, stop editing! Happy blogging. */

For more information about the Builder Preview messages, please check this out:

Let us know how it goes.

Hello Prasant :slight_smile: ! Thanks for these advices.

A feedback first :

  • There is no change if a turn off all the others extensions
  • The theme I use is the orignal one, not a child one. I don’t do customization because i don’t know how ;).
  • I also added the memory extension code as you suggested (wp-config.php code is listed at the end of my post).
  • The editing function works with a new page just created. But not for existing pages.

Concerning the debug things : I could find WP_DEBUG but not WP_DEBUG_LOG so I add it myself in wp-config.php:

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

And here is the content of debug.log, does it give any relevant information ?

[06-Jan-2018 07:43:44 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:43:44 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:43:46 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:43:48 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:43:51 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:44:02 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:44:04 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:44:07 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:44:08 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:45:06 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:45:06 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111
[06-Jan-2018 07:48:31 UTC] PHP Notice:  Constant WP_POST_REVISIONS already defined in /home/httpd/j/u/l/julien777/ on line 111

Here is the wp-config.php code (without DB access information) :


// BEGIN iThemes Security - Ne pas modifier ou supprimer cette ligne
// iThemes Security Config Details: 2
define( 'DISALLOW_FILE_EDIT', true ); // Désactiver l’éditeur de fichier - Sécurité > Réglages > Modifications de WordPress > Éditeur de fichier
// END iThemes Security - Ne pas modifier ou supprimer cette ligne

define('WP_CACHE', true); // Added by WP Rocket

/** Enable W3 Total Cache Edge Mode */

define('W3TC_EDGE_MODE', true); // Added by W3 Total Cache

 * La configuration de base de votre installation WordPress.
 * Le script de création wp-config.php utilise ce fichier lors de l'installation.
 * Vous n'avez pas Ă  utiliser l'interface web, vous pouvez directement
 * renommer ce fichier en "wp-config.php" et remplir les variables Ă  la main.
 * Ce fichier contient les configurations suivantes :
 * * réglages MySQL ;
 * * clefs secrètes ;
 * * préfixe de tables de la base de données ;
 * @link 
 * @package WordPress

// ** Réglages MySQL - Votre hébergeur doit vous fournir ces informations. ** //
/** Nom de la base de données de WordPress. */
define('DB_NAME', '*************');

/** Utilisateur de la base de données MySQL. */
define('DB_USER', '*************');

/** Mot de passe de la base de données MySQL. */
define('DB_PASSWORD', '*************');

/** Adresse de l'hébergement MySQL. */
define('DB_HOST', '');

/** Jeu de caractères à utiliser par la base de données lors de la création des tables. */
define('DB_CHARSET', 'utf8mb4');

/** Type de collation de la base de données. 
  * N'y touchez que si vous savez ce que vous faites. 
define('DB_COLLATE', '');

 * Clefs uniques d'authentification et salage.
 * Remplacez les valeurs par défaut par des phrases uniques !
 * Vous pouvez générer des phrases aléatoires en utilisant 
 * {@link le service de clefs secrètes de}.
 * Vous pouvez modifier ces phrases Ă  n'importe quel moment, afin d'invalider tous les cookies existants.
 * Cela forcera Ă©galement tous les utilisateurs Ă  se reconnecter.
 * @since 2.6.0
define('AUTH_KEY',         '0BP[41L0w/DWj3G4f~J3%Np-c,.^mR<@&JZI./,s>y$e{h9<*fXVS@EV9Ay-&rVW');
define('SECURE_AUTH_KEY',  '0g;Xd[$?lRd Y!<D^Q+vqp^+Qb7uto^(v9DyWfw7Wz6h/ZL$cw/sM#e{%~i,[[%h');
define('LOGGED_IN_KEY',    'VfGdl2~8{D$[}m1:IYk(zp9b]&/@4@)m*np;%[Z4qARgMf?)4j2}yx;lb}+627&I');
define('NONCE_KEY',        '(>zW)=n/l5dY`cFAl>qJsiVu/H[0a4>(YuDGeRDpiH@*KfgV w;sENMC(y{(}-1O');
define('AUTH_SALT',        'c|(hHkwQS.v{cBJcYBu}#6rV|gB({{u;*a?nkv43s+Run]w!oQ1}i*K +!*#1a5G');
define('SECURE_AUTH_SALT', 'a4Ul[k#e.syjfV)u/JkgpVgbt[%([In]?7 =^#}@:o_?95t6bE!r+*se5,+RD?FB');
define('LOGGED_IN_SALT',   '6EmJecj/q:,+YpRZTq%E,,J1|ufttKV+#8v*`E%[x!~)]pHHFk~Bfh{.C<qVE~He');
define('NONCE_SALT',       'F2=c<1{rz0 n$GUgQrIWzwS1q9iUGQZ!eJ#?.3pwpoJ|V}//hFUG2 <*8cAbS+@X');

 * Préfixe de base de données pour les tables de WordPress.
 * Vous pouvez installer plusieurs WordPress sur une seule base de données
 * si vous leur donnez chacune un préfixe unique. 
 * N'utilisez que des chiffres, des lettres non-accentuées, et des caractères soulignés!
$table_prefix  = 'et_';

 * Pour les développeurs : le mode déboguage de WordPress.
 * En passant la valeur suivante Ă  "true", vous activez l'affichage des
 * notifications d'erreurs pendant votre essais.
 * Il est fortemment recommandé que les développeurs d'extensions et
 * de thèmes se servent de WP_DEBUG dans leur environnement de 
 * développement.
 * Pour obtenir plus d'information sur les constantes 
 * qui peuvent être utilisée pour le déboguage, consultez le Codex.
 * @link 
define('WP_DEBUG', true);
define( 'WP_DEBUG_LOG', true );

define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );

/* C'est tout, ne touchez pas Ă  ce qui suit ! Bon blogging ! */

/** Chemin absolu vers le dossier de WordPress. */
if ( !defined('ABSPATH') )
	define('ABSPATH', dirname(__FILE__) . '/');

/** RĂ©glage des variables de WordPress et de ses fichiers inclus. */
require_once(ABSPATH . 'wp-settings.php');/** Suppression des révisions WordPress. */ define( 'WP_POST_REVISIONS', false );

/** Correction du bug des 10 secondes dans BackWPup */
define( 'ALTERNATE_WP_CRON', true );

Hi there,

Actually, the error message did not give any clue.

kindly get back to us with the URL/User/Pass of your WordPress dashboard using the Secure Note functionality of the post to follow up the case.

Also, name a page which we can test the case.

Thank you.

You’ll find the information in secure notes.

All the published and draft pages can test the case. I am actually working on Accueil.

Hi there,

Please change your debug lines to this

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

The purpose of that is to log it and prevent the messages displaying in the browser and to ajax responses. No reason to display it :slight_smile:

And please provide your FTP login credentials so I can check it directly. And since we’re troubleshooting, please disable all the cache feature and rocket loader.


Hello Rad,

debug lines are now changed as suggested.
WP Rocket is now turned off. I don’t see any other cache feature.

FTP logs are in secure notes.

Thanks !

Hi there,

Are you on shared hosting? It’s random, there are times it will load instantly and sometimes it won’t. If you’re on shared hosting then I think other sites performance from the same machine is affecting your site. That’s mostly the problem with shared hosting.

Screenshot in the secure note.

Plus, the FTP login credentials are incorrect. Please provide the correct one.


Thanks Rad,

I also noticed it’s random. The hosting is indeed a shared hosting. How does it matter ?

By the way, all apologize, the FTP data I sent are old. Here are the correct ones.


Hey There,

Shared hosting is associated with limited hardware use. Given that all the server resources have to be divided up among the various hosted websites, users of this hosting model can only take advantage of a portion of the server’s overall capacity. Following this, when one site on the hosting platform experiences a large amount of traffic, this heavy workload may have a negative effect on other websites hosted on the same server. Depending on the service model, however, shared hosting users are guaranteed a minimum performance, which in turn ensures a smooth and stable experience. User accessed management and administrative functions are significantly limited with this model. Fundamental hardware configuration that affect users is left entirely up to the provider. These are some most prominent differences between shared hosting and other options, like virtual and dedicated servers (which normally provide users with root access).

I have checked your wp-config.php and it seems memory limit is in place. I just noticed that you are using WP Rocket and WP Autoptimize. Please disable this plugins temporarily. These plugins are best recommended after you have finished developing your site or ready to go live.

Hope this helps.

Ok thanks. It’s still random even with these 2 extensions disabled.

Do you have any additional suggestion ?

Hi there,

The problem was that you did not purge the cache before deactivating the Wp Rocket plugin. I purged the cache and deactivated, I managed to access the homepage using the Cornerstone and change a section and add extra dots:

That is working correctly now, you need to make sure that you clear your browser cache to see the result live.

Thank you.

Hello Christopher,

it looks like working very well now. Thanks so much !

  • Is it in the WP Rocket options that you were able to purge the cache ?
  • If I understand well, you advise me to disable all this cache features during my work and to enable them again as soon as I will not work on the website any more, right ?


Hi there,

Yes the steps should be as follows: (having in mind that Wp Rocket is active)

  1. You purge the cache of the WP Rocket from the top section of the dashboard which says WP Rocket you will see a drop-down which says purge cache.

  2. You go to plugins menu and deactivate the WP Rocket plugin

  3. You clear your browser cache

  4. Go to the page and using Cornerstone edit stuff and save

  5. Check the result on the front end

  6. Activate WP Rocket plugin again.


You’re all awsome guys. It’s really helpful !
Lots of gratitude. To me, the topic can be now closed.

Take care.

You’re welcome, Julien.

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