Outlook prompts for credentials when an Exchange Server 2010 CAS restarts

Consider the following scenario:

• A Microsoft Exchange Server 2010 server has the Client Access server (CAS) role assigned.
• The Exchange Server 2010 CAS is a member of Client Access Array.
• The CAS is shut down or restarted.
• A Microsoft Outlook client tries to connect to the CAS through a server that has Network Load Balancing (NLB) configured. The Outlook client has connected to the CAS before.

In this scenario, the RPC service on the CAS shuts down any existing connections, and sends a reset notification to clients. When a client tries to create a new connection, the new connection fails because the CAS is not accepting new connections. Therefore, the client prompts the user for credentials.

This issue occurs because services on the CAS are stopped when it is shut down or restarted. However, the network load balancer does not recognize that the services are offline.

To prevent this issue, do not let the CAS accept new connections from the load balancer before the CAS is shut down or restarted. For example, issue a drainstop command to the server in Network Load Balancing Manager.

To work around this issue, cancel the credential request, and then restart the Outlook client. After all clients have disconnected from the CAS, shut down or restart the server.

For information about an issue that can occur when you try to connect to an Exchange mailbox by using Microsoft Outlook 2007, click the following article number to go to the article in the Microsoft Knowledge Base:

For information about an issue in which you are repeatedly prompted for a password in Outlook 2007, click the followng article number to go to the article in the Microsoft Knowledge Base:

For information about an issue in which you are prompted for credentials in Outlook 2007 after an Exchange CAS is restarted, click the following article number to go to the article in the Microsoft Knowledge Base:

For more information about load balancing in Exchange Server 2010, go to the following TechNet website:For general information about load balancing, go to the following TechNet website: