W3 Total Cache plugin HTACCESS Header Has Too Many Arguments

We have seen several WordPress sites go down with an Internal Server Error. Frontend and backend of WordPress not working. Server error log indicates an issue with HTACCESS file.

.htaccess: Header has too many arguments

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Quick Fix: Restore HTACCESS file to default and deactivate W3 Total Cache Plugin

In order to fix you should restore the HTACCESS file to a default WordPress version. The W3 Total Cache plugin may break the site again by adding the custom lines back into the HTACCESS file. This issue has been documented on WordPress support thread:

https://wordpress.org/support/topic/error-in-htaccess-after-updating-to-v2-8-0/#post-18232367

You also may need to deactivate W3 Total Cache plugin. If the website is down, you can do this via FTP access by re naming the W3 Total Cache plugin. Go to wp-content/plugins/ and rename w3-total-cache folder to w3-total-cache2 or any new name. This will force WordPress to deactivate the plugin. WordPress and the website will now be working again.

How to Fix the HTACCESS W3 Total Cache Issue

You will need to get the plugin running again and keep it from writing to the HTACCESS file.

1. Change permissions on .HTACCESS file in website root directory so the w3tc plugin doesn’t keep writing to the file and taking the site down. Remove all w3tc lines. Or just remove the problem line Public-Key-Pins. This entry is what seems to be taking the websites down

Header set Public-Key-Pins “pin-sha256=”$pin”; pin-sha256=”$pinbak”; max-age=31536000″

1. Delete the cache folder and w3tc-config folder completely in the wp-content folder. You will need FTP access. Navigate to wp-content folder and remove W3 Total Cache folders. Perhaps these settings directories just need to be cleaned out and rebuilt from scratch. This would be the same as re installing the plugin. Just make sure to remove those folders completely.
2. Now you can run the w3tc plugin and adjust your settings. Double check everything. Turn off the security headers if you want. One of the settings with security headers seems to be the problem.
3. Change permissions on .HTACCESS back to www-data. Let the plugin write to .HTACCESS

Now everything is working again with w3tc running.