Error after upgrading to 2.5

The blog can be viewed, but I get this error message when logging into dashboard:

Fatal error: Call to undefined function: wp_register_sidebar_widget() in /home/content/p/e/t/peterish/html/wordpress/wp-admin/includes/dashboard.php on line 31

What does this mean? It occured after I manually upgraded on my godaddy server…something probably got messed up?