Symptoms
When you try to open Microsoft Office documents from a Microsoft SharePoint site that was published through Microsoft Forefront Unified Access Gateway 2010, you may receive multiple authentication prompts before the document opens.
This issue occurs only if you try to access the document directly before you access any other page on the SharePoint site. For example, this issue may occur if you try to access a specific document that you bookmarked. This issue does not occur if you first browse to the SharePoint homepage, the root of the document library, or any other page on the SharePoint site.
Cause
This issue occurs because Unified Access Gateway uses a persistent session cookie to allow for single sign-on (SSO) when you transition from a web browser into an Office application. This cookie is generated on the client by injecting a piece of JavaScript into the response stream when the client requests the Core.js file from the SharePoint server. Because this JavaScript file is included in all SharePoint pages, the Unified Access Gateway cookie should always be created. However, if you access the document directly and do not browse first to another SharePoint page, the client does not request the Core.js file, and the cookie is not set. This issue causes a problem for SSO authentication.
Resolution
To resolve this problem, install the service pack that is described in the following Microsoft Knowledge Base article:
2710791 Description of Service Pack 2 for Forefront Unified Access Gateway 2010
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
