WPMU 2.8.1 Upgrade issue

After upgrading I'm experiencing issues with Wordpress 2.8.1.

After upgrading to 2.8.1, upgrade was successful but I had this error message in footer.

Fatal error: Call to undefined function compression_test() in C:\wamp\www\wpmu\wp-admin\admin-footer.php on line 38.

The upgrade banner doesn't go away.