Illegal string offset 'sidebar' error on some pages

Have you tried:

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the default theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

– re-uploading all files & folders – except the wp-content folder and wp-config.php & root .htaccess files – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.

That’s actually a warning, not an error, so it won’t cause a runtime error.

Error: Fatal run-time errors. These indicate errors that can not be recovered from, such as a memory allocation problem. Execution of the script is halted.

Warning: Run-time warnings (non-fatal errors). Execution of the script is not halted.

This also tells me you’re running your WordPress site with debug mode on, which is not a good practice.

In wp-config.php, change:

define('WP_DEBUG', true);

to:

define('WP_DEBUG', false);

As far as the warning message itself:

Warning: Illegal string offset 'sidebar'

This generally means that your code is trying to access a key in an array that doesn’t exist. The theme author needs to fix that by checking that a key in the array exists (is_set) before trying to access it.

It does indicate a problem with the code, but not a fatal one. I often see piles of Warning messages from various plugins when I turn on DEBUG. (which doesn’t make it right, but sadly it isn’t uncommon) At the very least, set DEBUG to false so the Warnings won’t display on your production site.