Event ID : 9186

Issue : System Attendant has detected that the local computer is not a member of group.

Event Source: MSExchangeSA

Cause :
The Exchange Server computer's distinguished name has been changed. When System Attendant starts, it caches the distinguished name of the local computer. The Exchange Server computer's distinguished name changes when it is moved from one organizational unit to another organizational unit. The new distinguished name is different from the distinguished name that is in the cache. Therefore, System Attendant logs event ID 9186 and 9187 messages.

Description: Microsoft Exchange System Attendant has detected that the local computer is not a member of group 'cn=Exchange Domain Servers,cn=Users,dc=microsoft,dc=com'.System Attendant is going to add the local computer into the group. The current members of the group are 'CN=SERVERNAME,OU=NEWOU,DC=microsoft,DC=com; '.

Action Required :
Method 1
Restart System Attendant to refresh the cached value.
Note You must restart the following services that depend on the System Attendant service:
1.Microsoft Exchange Information Store
2.Microsoft Exchange Message Transfer Agent (MTA) Stacks
3.Microsoft Exchange Event
4.Microsoft Exchange Internet Message Access Protocol, Version 4rev1 (IMAP4)
5.Microsoft Exchange Post Office Protocol version 3 (POP3)
Method 2
If your Exchange Server computer is not listed, follow these steps:
1.Remove the Exchange Server computer account from the Exchange Domain Servers group.
2.Add the Exchange Server computer account back.
3.Restart System Attendant.

Ref.Link : http://support.microsoft.com/kb/271335