User Avatar plugin not working since upgrading to 3.0

Clicking on the Edit link in the Avatar column on the Super Admin/Users page returns "Apologies, but the page you requested could not be found. Perhaps searching will help."

The page it's trying to access is http://davidjames.realestatetribe.com.au/wp-admin/wpmu-admin.php?page=edit-user-avatar&uid=14

I had a similar problem with the Messaging plugin. The issue was resolved by replacing inbox.php, which was deleted when wp-admin was deleted as per the instructions at https://premium.wpmudev.org/blog/how-to-upgrade-wpmu-2-9-2-to-wordpress-3-0-in-5-easy-steps/.

I have checked and options-discussion.php is in the wp-admin folder as per the plugin installation instructions.

Any help would be greatly appreciated.

Peter