The “unexpected output” forces PHP to send HTTP headers right before the output is sent, and that’s too early for WordPress, which can’t send cookies later as they are HTTP headers too.
If you look at your site, you get a bunch of notices at the top, which means you have something like …
define( 'WP_DEBUG', true );
… in your wp-config.php
. You should never set that to true
on a live site.
So how to fix it? Two steps:
-
Access your site per FTP or SSH, and edit the
wp-config.php
, soWP_DEBUG
is set tofalse
. -
Then log in, and update WordPress. Newer versions won’t have this problem.
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