If you use thematic child themes and receive the following error on WordPress 3.4 & Thematic upgrades
Call to undefined function thematic_canonical_url() .. line 25 ..
the function was deprecated and is no longer necessary, but it may still be lingering in your child theme’s header.php file.
In your child theme header.php file, delete the following from lines 24-25
// Creating the canonical URL
Now you should be back in business!