Errors after upgrade to wordpress 4.2

I have exactly the same problem. Would like to know the solution as well. Thank you.

Update: so since WordPress 4.2 is pushing this message as a notice, you can turn it off if you disable debug mode.
Add this to your wp-config.php
define('WP_DEBUG', false);

But the real solution is to add an id to the register_sidebar functions.
https://wordpress.org/support/topic/error-after-updating-to-42

It would be nice if the kriesi.at crew would fix this asap :)

• This reply was modified 9 years, 6 months ago by envis.

I’m getting a similar thing with a header warning at end.

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Displayed Everywhere” sidebar. Defaulting to “sidebar-1”. Manually set the id to “sidebar-1” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Sidebar Blog” sidebar. Defaulting to “sidebar-2”. Manually set the id to “sidebar-2” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Sidebar Pages” sidebar. Defaulting to “sidebar-3”. Manually set the id to “sidebar-3” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Footer – column1” sidebar. Defaulting to “sidebar-4”. Manually set the id to “sidebar-4” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Footer – column2” sidebar. Defaulting to “sidebar-5”. Manually set the id to “sidebar-5” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Notice: register_sidebar was called incorrectly. No id was set in the arguments array for the “Forum” sidebar. Defaulting to “sidebar-6”. Manually set the id to “sidebar-6” to silence this notice and keep existing sidebar content. Please see Debugging in WordPress for more information. (This message was added in version 4.2.0.) in /home/content/30/7792830/html/wp-includes/functions.php on line 3560

Warning: Cannot modify header information – headers already sent by (output started at /home/content/30/7792830/html/wp-includes/functions.php:3560) in /home/content/30/7792830/html/wp-includes/pluggable.php on line 1196

I can see my website but I can’t access my site, please advise.