Upgrade to 2.5.1 dashboard.php fatal error

My blog is hosted at Bluehost. I upgrade WP using fantastico, which is provided by Bluehost, everytime a new version is available. When I upgraded from 2.3.3 to 2.5.1 this week I got the following : Fatal Error: Call to undefined function wp_register_sidebar_widget() in /home/flamestv/public_html/wp-admin/includes/dashboard.php on line 32. Why do I have a dashboard.php problem, and more importantly, I’m stuck. How can I correct this? Of course I would like to be able to fix this without loosing everything. Any suggestions? Thanks