20KDCThe currently selected KDC certificate was once valid, but now is invalid and no suitable replacement was found. Smartcard logon may not function correctly if this problem is not remedied. Have the system administrator check on the state of the domain's public key infrastructure. The chain status is in the error data.
If an Active Directory CA was removed, Domain Controllers will display this error until they get a new certificate from a different CA.
Run "certutil -dcinfo deleteBad" to remove the offending certificates. The DCs should then get new ones the next time Autoenrollment runs.