Sorry… forgot to add the file info where to comment out:
/wp-includes/widgets.php on line 825
I just commented out since i don’t use side widgets. I deactivated all plugins as well and continued to get an error.
This helped my situation:
//if ( empty($wp_registered_sidebars[$index]) || !array_key_exists($index, $sidebars_widgets) || !is_array($sidebars_widgets[$index]) || empty($sidebars_widgets[$index]) )
//return false;