While trying to build a Kerberos ticket, the Key Distribution Center (KDC) detected two user objects with the same user principal name (UPN). The KDC cannot determine which user object is correct; therefore, it cannot create a ticket.

The Users and Computers Microsoft Management Console (MMC) snap-in checks for this problem and attempts to prevent it from occurring. However, the following situations can create this condition:

• A script that is being used to create users is not checking for uniqueness.

• A Microsoft® Windows® NT 4.0 utility is being used to create users.

• A metadirectory or other provisioning tool that is being used to create users is not checking for uniqueness.

• Replication is slow or malfunctioning.

• A denial-of-service attack is under way.

Change the UPN on one of the conflicted user objects using the Users and Computers snap-in.

For more information, see:

• Microsoft Help and Support for Microsoft Windows Server 2008 and above

• Microsoft Knowledge Base