You must have deleted users using joomla/mambo user management instead of Community Builder one.

To find the list of which ones, this SQL query, that you can execute in phpMyAdmin, will tell you:
[code:1]SELECT c.id FROM jos_comprofiler c LEFT JOIN jos_users u ON u.id = c.id WHERE u.id IS NULL
[/code:1]

I added to upcoming CB 1.0 stable's sychronization tool the deletion of these CB entries corresponding to missing users. The fix is to big to be shown here.