Imported Users

I used the Import Users from CSV plugin to import all of the users for a new installation. Less than 10 users were created manually. The Co-Authors Plus plugin autocomplete only seems to work if I am searching for a user that was manually created. It doesn’t work if I am searching for one of the 500+ users that were imported. What do I need to do to get the Co-Authors Plus plugin autocomplete to search for all users and not just the users that were created manually?

http://wordpress.org/plugins/co-authors-plus/