Event ID - 9551

Event Id9551
SourceMSExchangeIS Mailbox Store
DescriptionAn error occurred while upgrading the ACL on folder [MBX:User1]/Calendar located on database "Server1\Mailbox Store 1 (server)". The Information Store was unable to convert the security for /O=ORGANIZATION/OU=SITE/CN=RECIPIENTS/CN=123456 into an NT Security Identifier. It is possible that this is caused by latency in the Active Directory Service, if so, wait until the user record is replicated to the Active Directory and attempt to access the folder (it will be upgraded in place). If the specified object does NOT get replicated to the Active Directory, use the Microsoft Exchange System Manager or the Exchange Client to update the ACL on the folder manually. The access rights in the ACE for this DN were 0x401.
Event InformationIf you use an administrator account to run Exmerge.exe to identify user accounts that are not represented in Active Directory, the event ID 9551 warning messages that identify those objects and users may not be logged.
RESOLUTION: To resolve this problem, obtain the latest service pack for Microsoft Exchange 2000 Server.
Reference LinksXADM: Event ID 9551 Warning Messages Are Not Logged If You Run Exmerge

XADM: Migrated Exchange Server 5.5 Mailboxes Generate Event ID 9551 Warning Messages for the ACL

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