In a mixed Microsoft Exchange Server 2003 and Microsoft Exchange Server 2007 environment, you have more than one Administrative Group. The network connections between these Administrative Groups are low in bandwidth.
Public Folder replication is scheduled among the Administrative Groups.
An Exchange Server 2007 user creates an appointment or a meeting request in Microsoft Office Outlook 2007. Then, the Exchange Server 2007 user invites an Exchange Server 2003 user to this appointment or meeting as an attendee.
The Exchange Server 2003 attendee belongs to a different AG than the Exchange Server 2007 user.
The Exchange Server 2007 user checks the Free/Busy information in Office Outlook 2007.
In this scenario, the Exchange Server 2007 user intermittently cannot access the Exchange Server 2003 server user's Free/Busy information.
If a user in an Exchange Server 2007 Administrative Group requests the Free/Busy information for a user in an Exchange Server 2003 Administrative Group, Exchange Server 2007 Client Access Service (CAS) uses an Exchange Web Service (EWS) proxy. Therefore, the request may use the low bandwidth connection to the Exchange Server 2003 Administrative Group. In this case, the Free/Busy information may be unavailable intermittently because of the low network bandwidth.
To resolve this problem, follow these steps:
Install Update Rollup 2 for Exchange Server 2007 Service Pack 2 on the Exchange server.
972076 Description of Update Rollup 2 for Exchange Server Service Pack 2
Locate the Web.config file in the following folder: %ProgramFiles%\Microsoft\Exchange Server\ClientAccess\exchweb\EWS
Open the Web.config file in Notepad, and then locate and add the following line between the <appsettings> element and the </appsettings> element:
Note If the value of the key "UseLocalReplicaForFreeBusy" is true, Exchange Server 2007 CAS checks if there is a replica for the Exchange Server 2003 users on a local public folder server. If there is a replica available, Exchange Server 2007 CAS uses the replica instead of a low bandwidth WAN connection.
Save the Web.config file and then restart the Exchange Web Service on the Exchange Server 2007 server.
Do the same change in the Web.config file located in: %ProgramFiles%\Microsoft\Exchange Server\ClientAccess\OWA
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.