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Additional authentication prompt is displayed when an external network user signs in to an Office Communicator 2007 client
Article ID: 2633194 - View products that this article applies to.
When a user tries to sign in to a Microsoft Office Communicator 2007 client from an external network, an additional credential prompt is displayed to retrieve calendar data from Outlook.
This issue occurs because the Exchange Server 2007 Client Access server uses both Negotiate and NTLM protocols for authentication to return the available data back to the Office Communicator client. However, Office Communicator uses the NTLM protocol only to negotiate authentication. Therefore, an additional authentication is requested.
To work around this issue, follow any of these steps.
Workaround 1: Enable Integrated Windows Authentication in Internet ExplorerYou can retrieve available data through the Autodiscover service on the Office Communicator client. To do this, follow these steps:
Workaround 2: Use Registry EditorImportant This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756You can use Registry Editor to enable the NTLM authentication on the Office Communicator client. To do this, follow these steps:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
Workaround 3: Use Internet Information ServicesYou can instruct Internet Information Services on the Exchange Server 2007 Client Access server to set NTLM as the first authentication provider in the WWW-Authenticate header. To do this, use the appropriate method for the version of IIS that you have.
For Internet Information Services 6.0
For Internet Information Services 7.0
For more information about the Autodiscover service, visit the following Microsoft website:
General information about the Autodiscover service
For more information about the Integrated Windows authentication, visit the following Microsoft website:
General information about the Integrated Windows authentication
Article ID: 2633194 - Last Review: January 28, 2013 - Revision: 2.0