After performing a WordPress upgrade to 3.3.1, I can no longer access the administration interface. The website works fine, but when I click on Dashboard, I receive the following error:
Fatal error: Call to undefined function _wp_admin_html_begin() in /home/a7938356/public_html/wp-admin/admin-header.php on line 40
... help! What can I do? I don't have a lot of content, so I could reinstall WordPress, but I'd like to know what went wrong and prevent it in the future.