Event ID : 8026

Issue : Exchange failing to establish connectivlity with domain controllers.

Event Source : MSExchangeAL

Cause : After you run dcpromo to demote a Windows domain controller (DC) in your domain, the Microsoft Exchange 2000 Server or Microsoft Exchange Server 2003 MSExchangeAL service starts to log events 8026 and 8260 every 10 minutes.

Description : LDAP Bind was unsuccessful on directory for distinguished name ''. Directory returned error: []

Action Required : Connect to exchange and verify connectivity to Domain Controllers, run netdiag tool to verify connectivlity and secure channel .

Ref.Link : http://support.microsoft.com/kb/272552