How to Fix WordPress W3 Total Cache Uncaught Exception Unknown Engine 500 Fatal Error

How-to-Fix-WordPress-W3-Total-Cache-Uncaught-Exception-Unknown-Engine-500-Fatal-Error

Recently, We are facing an annoying problem when installing and activating W3 Total Cache (W3TC) plugin on WordPress or after updating W3 Total Cache (W3TC) Plugin.

After installing and activating the plugin we are facing this problem: “Uncaught Exception Unknown Engine 500 Fatal Error”.

And when we are trying to add a new post or updating a post or page or anything from the WordPress dashboard we see a white screen. It’s really very annoying. Is it not?

The problem is caused by a new feature called FSD CDN implemented by W3 Total Cache in version 0.9.6. FSD (Full Site Delivery) is a feature to host the whole website with a full site content delivery network provider to reduce the page load time, so that whole website will appear to load instantly for site visitors.

However, for an unknown reason, the FSD CDN feature in W3TC is enabled and activated by default, with Cloudflare (other FSD CDN types are Amazon CloudFront, Limelight, and MaxCDN) chosen as the FSD CDN service provider, even though the feature is only available after the upgrade.

Ok, now we are trying to fix this issue now.

Step 1: Go to your Cpanel or login it from FTP. Then find the “wp-config.php” file and open it.

Step 2: Find this line from your “wp-config.php” file:

define(‘WP_DEBUG’, false);

make it true instead of false:

define(‘WP_DEBUG’, true);

Also, add this 2 line above this:

error_reporting(E_ALL);

ini_set(‘display_errors’, 1);

Then go to your WordPress dashboard and try to add a new post or update something, Now you can able to see the exact error that happens when trying to update it.

Solution:

The FSD CDN option in General Settings of W3 Total Cache is grayed out and disabled though. Thus, to resolve the issue, SSH into the webserver,

and edit the ..wp-content/w3tc-config/master.php file.

Search for the section for cdnfsd, and set the cdnfsd.enabled to “0” or FALSE.

“cdnfsd.enabled”: “0”,
“cdnfsd.engine”: “”,
“cdnfsd.debug”: false,

As the FSD CDN field on the WP admin panel is defaulted to True, the setting will revert to “1” or “True” (which enables the FSD CDN and causes the error) on every save of W3TC settings. So remember to change the value after you save any settings of W3 Total Cache.

ALTERNATIVE

If the setting to disable the FSD CDN does not stick or fail to solve the error, you can roll back to the previous stable version of W3 Total Cache, that’s version 0.9.5.4. You need to manually delete the currently installed W3 Total Cache, and then upload the old version of W3TC before activating it.

Thanks for reading the post. Take Care!

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