If you previously used a version of Messaging Server 5 or Calendar Server 5, your LDAP entries were formatted Schema 1. In your new Calendar Server 6 2005Q4 environment, if you are going to use Access Manager for authentication, you must convert your LDAP entries to Schema 2 format by running this utility.
If you are not using Access Manager, you should still consider migrating your LDAP data, since Schema 2 is the preferred LDAP mode for all Java Enterprise System products that use LDAP. In the future it is possible that newer versions of the communications products (Calendar, Messaging and Instant Messaging) may not support Schema 1. However, the migration can be deferred until a later, more convenient time if you are not going to be using Access Manager at this time.
If you have a separate LDAP directory for preferences, you must run commdirmig on that LDAP as well as the one used for authentication.