I've updated my site http://www.velo-classique.com/ to the newest version of WP. The theme and all the plugins are updated but I get the following errors:

  • Cookie error when login.
  • When I save, for example, Writting options in WP Dashboard it redirects to a blank page.
  • The velo-classique.com don't redirect to www.velo-classique.com.

I've checked the database, the wp-config.php and many thing that I've read on the Internet and troubleshooting section of WordPress and nothing works.

What can it be?

  • WP core is exceptionally backwards compatible. What was the previous core version and did you update regularly? Loose guess is either core was modified or extensions in use are too old (/too bad) to handle upgrade.
    – Rarst
    Sep 13 '16 at 18:26

There are newlines being generated before your <!DOCTYPE> declaration, which you can see by viewing the source code of your site from your browser:

enter image description here

As Rarst suggested, there is probably some incompatible code that is causing this output to be generated. The extra whitespace can cause the issues you've described.

There are many resources on this site and others about troubleshooting whitespace appearing before the doctype declaration.

  • 1
    Thank you. A plugin caused this error. But it is weird, it was updated and just deleted the files and reinstalled it again. Sep 15 '16 at 8:08

Please check this on your wp-config.php file:

define('COOKIE_DOMAIN', 'http://www.example.com/');

If it there, remove it.

  • I've already done it and nothing. Thanks for your suggestion. Sep 14 '16 at 7:35

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