I get this error on page 1 of the category archives:
Warning: rtrim() expects parameter 1 to be string, object given in example.com/wp-includes/formatting.php on line 1381
This comes from using the category slug:
example.com/example-–-stuff-and-stuff/ (note the ---)
WordPress processes this just fine. Yoast WP SEO causes this error on page 1 of the archives by category page.
Page 2 adds this error:
Catchable fatal error: Object of class WP_Error could not be converted to string in example.com/wp-content/plugins/wordpress-seo/frontend/class-frontend.php on line 735
I know that this is a WP SEO error because if I deactivate WP SEO, I don't get the error.