Hi Everyone, I am experiencing an issue with Exchange 2010 standard rollup 2 running, namely accessing shared Calendars I have two servers in the Main AD site, one virtual server running 2008 R2 standard with the CAS and HT roles, and a physical mailbox server running on 2008 R2 Enterprise. There is another physical server in the DR AD site running 2008 R2 Enterprise with all exchange roles. All servers are in production in a 2003 domain (2 DC in the main site and 1 in the DR site all running 2003 R2 SP3) with 2 exchange 2003 SP2 servers (front end and back end) still running and with some mailboxes still not migrated. I have one DAG group set-up on the mailbox servers and two Databases that are replicated from the main mailbox server to the DR server and are both healthy with no queues. Clients are using mostly Outlook 2003 with encryption enabled in cached mode. When users try to access a shared calendar they receive the following message The connection to the Microsoft Exchange server is unavailable Outlook must be on line or connected to complete this action At the same time if I open a User's mailbox properties in the EMC and click on the Calendar Settings Tab I receive another error this time saying: Cannot open mailbox /o=domain/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)cn=configuration/cn=servers/cn=MAILSERVER/cn=Microsoft System Attendant. it was running the command Get-CalendarProcessing -Identity 'Domain/OU/OU/users' -ReadFromDomainController If I rerun this command from the EMS is see the follwing extra information Get-CalendarProcessing -Identity 'OU/OU/users' -ReadFromDomainController Cannot open mailbox /o=DOMAIN/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=MAILSERVER/cn=Microsoft System Attendant. + CategoryInfo : NotSpecified: (0:Int32) [Get-CalendarProcessing], TooManyObjectsOpenedException + FullyQualifiedErrorId : 33587F8C,Microsoft.Exchange.Management.RecipientTasks.GetMailboxCalendarSettings I also see lots of event id 102 MSExchange Search Indexer Exchange Search Indexer has failed to crawl the mailbox etc etc Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException: Cannot open mailbox /o=DOMAIN/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=MAILSERVER/cn=Microsoft System Attendant. ---> Microsoft.Mapi.MapiExceptionSessionLimit: MapiExceptionSessionLimit: Unable to open message store. (hr=0x80040112, ec=1246) These servers have been in production for about a month and this error first happened last week and was resolved by restarting the Mailbox server IS. Mail flow is working normally as is user’s access to their mailboxes. I have been looking at the following link http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/2b6fb514-34c8-488a-be4d-60c58ddd4a5a However what’s different between My setup to the one in the article, is that System Attendant is set to the Local Database on the both my Mailbox severs, I am wondering if this needs to be moved to either of the two DAG Mailstores or if it is fine where it is? And we only have a single AD forest/Domain setup and we are simply transitioning Exchange 2003 to 2010. Any help most gratefully received, I‘ve taken out our specific domain/user info and tried to make the post generic to make things easier.

Did you get this resolved? I am having the exact same issue on my server.

Hi Stephen, for us it turned out to be a misconfiguration of new HA Blackberry Enterprise Server running version 5 that was creating so many connections to the exchange servers that when lots of users we working on the system it meant we hit an in build limit for exchange and no one could access calendar settings for other users and the error appeared in the EMC too. I don't know the exact BES server details however sorry. HTH