Undefined index: leaderboard in page--full-width-wrappers.tpl.php

I think this is unlikely to be a bug in the core theme - since you upgraded can you check if you have the region declaration in your sub-themes info file:

regions[leaderboard] = Leaderboard

If that is missing, and this region is not something you orindarily use in this theme, then you need to remove it from the page template.

You can do this by copying the page--full-width-wrappers.tpl.php file from at_core/templates to your sub-theme and deleting this out of the template, it near the top, around line 92:

  <?php if($page['leaderboard']): ?>
    <div id="leaderboard-wrapper"><div class="container clearfix">
      <?php print render($page['leaderboard']); ?>
    </div></div>
  <?php endif; ?>

Assuming fixed. Can't reproduce this in the theme and the region certainly exists.

I got this too, with Footheme, when I enabled "Use page--full-width-wrappers.tpl.php by default." You're right - that region does not exist in Corolla. When I added it to the .info file, the error went away.

Notice: Undefined index: leaderboard in include() (line 104 of /var/www/vhosts/INSTALL/sites/all/themes/adaptivetheme/at_core/templates/page--full-width-wrappers.tpl.php).

Had the same issue with the above message appearing on both front end and back end pages. Drupal 7 clean install with ATCommerce Theme, and I suspect using Panels (Everywhere) triggered it.

Either way, commenting the relevant lines (101 through 110) out in the referenced file solved the problem without any side-effects as far as I can see.

removing specific account folder names