I am experiencing an issue I can't find an explanation for. We are currently testing a new Exchange 2007 implementation running on Server 2008. We have two mailbox servers configuredas a CCR, and one server running both the Hub and CAS roles. We use a combination of Outlook 2007, Entourage 2008 and OWA clients as well as testing Macs new Exchange connectivity in Snow Leopard. When the mailbox service is running on the Preferred CCR node all of the mentioned clients work as expected. But when I failover to the passive node I am only able to connect to the mailbox service with the Outlook and OWA clients. Windows firewall is not runnig on either server and I have checked the Exchange services.I find the following entry in the security log on my passive node periodically, but it doesn't directly correspond to when I failover the mailbox service:Log Name: SecuritySource: Microsoft-Windows-Security-AuditingDate: 6/16/2009 10:30:25 AMEvent ID: 4625Task Category: LogonLevel: InformationKeywords: Audit FailureUser: N/AComputer: passivenode.hkusa.comDescription:An account failed to log on. Subject:Security ID:SYSTEMAccount Name:passivenode$Account Domain:HKUSALogon ID:0x3e7 Logon Type:3 Account For Which Logon Failed:Security ID:NULL SIDAccount Name:passivenode$Account Domain: Failure Information:Failure Reason:Unknown user name or bad password.Status:0xc000006dSub Status:0xc0000064 Process Information:Caller Process ID:0xaa0Caller Process Name:E:\Program Files\Microsoft\Exchange Server\Bin\Microsoft.Exchange.Search.ExSearch.exe Network Information:Workstation Name:passivenodeSource Network Address:-Source Port:- Detailed Authentication Information:Logon Process:Advapi Authentication Package:NegotiateTransited Services:-Package Name (NTLM only):-Key Length:0 This event is generated when a logon request fails. It is generated on the computer where access was attempted. The Subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe. The Logon Type field indicates the kind of logon that was requested. The most common types are 2 (interactive) and 3 (network). The Process Information fields indicate which account and process on the system requested the logon. The Network Information fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases. The authentication information fields provide detailed information about this specific logon request.- Transited services indicate which intermediate services have participated in this logon request.- Package name indicates which sub-protocol was used among the NTLM protocols.- Key length indicates the length of the generated session key. This will be 0 if no session key was requested.Event Xml:<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-a5ba-3e3b0328c30d}" /> <EventID>4625</EventID> <Version>0</Version> <Level>0</Level> <Task>12544</Task> <Opcode>0</Opcode> <Keywords>0x8010000000000000</Keywords> <TimeCreated SystemTime="2009-06-16T15:30:25.872Z" /> <EventRecordID>232684</EventRecordID> <Correlation /> <Execution ProcessID="680" ThreadID="2456" /> <Channel>Security</Channel> <Computer>passivenode.hkusa.com</Computer> <Security /> </System> <EventData> <Data Name="SubjectUserSid">S-1-5-18</Data> <Data Name="SubjectUserName">passivenode$</Data> <Data Name="SubjectDomainName">HKUSA</Data> <Data Name="SubjectLogonId">0x3e7</Data> <Data Name="TargetUserSid">S-1-0-0</Data> <Data Name="TargetUserName">passivenode$</Data> <Data Name="TargetDomainName"> </Data> <Data Name="Status">0xc000006d</Data> <Data Name="FailureReason">%%2313</Data> <Data Name="SubStatus">0xc0000064</Data> <Data Name="LogonType">3</Data> <Data Name="LogonProcessName">Advapi </Data> <Data Name="AuthenticationPackageName">Negotiate</Data> <Data Name="WorkstationName">passivenode</Data> <Data Name="TransmittedServices">-</Data> <Data Name="LmPackageName">-</Data> <Data Name="KeyLength">0</Data> <Data Name="ProcessId">0xaa0</Data> <Data Name="ProcessName">E:\Program Files\Microsoft\Exchange Server\Bin\Microsoft.Exchange.Search.ExSearch.exe</Data> <Data Name="IpAddress">-</Data> <Data Name="IpPort">-</Data> </EventData></Event>

Not sure if this helps but I've found these two articles related to entourage and exchange clusters:Entourage cannot send messages or receive messages after you fail over an active node to a passive node in an Exchange 2007 clusterhttp://support.microsoft.com/kb/941707You cannot connect to a clustered Exchange 2007 server through a server that has the Client Access Server (CAS) role installed by using the /exchange virtual directoryhttp://support.microsoft.com/kb/947802 Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator