WordpressMU upgrade from 2.8.1 to 2.8.2 function.copy error

I'm trying to use the automatic upgrade feature and get the following error message:

Warning: copy(.../wp-content/upgrade/wordpress-mu-2.8.2/wordpress/wp-admin/includes/update-core.php) [function.copy]: failed to open stream: No such file or directory in .../wp-admin/includes/class-wp-filesystem-direct.php on line 131

I've looked at the class-wp-filesystem-direct.php line 131 code and the entire section is the same as what is found on the 2.8 branch page here.

Never come across this error before. Any help would be much appreciated.