Error function wp_upgrade in wp-admin/upgrade line 89

After automatic upgrade from wp 3.0.3 to wordpress 3.3, in my Administrator page(wp-admin), WordPress suggest me to Upgrade database. But I got an error while upgrade.

Here is the error message : Fatal error: Call to undefined function wp_upgrade() in /home/my_website/public_html/wp-admin/upgrade.php on line 89

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I try to download fresh wordpress.3.3.zip, and upload all file exclude wp-content & wp-config.php.

But Still getting Error. How to solve my problem? Help me