Exchange Server 2010 users cannot open certain attachments when they access their mailboxes by using Outlook Web App

In a Microsoft Exchange Server 2010 environment, you have Microsoft Internet Security & Acceleration Server (ISA) 2006 SP1 installed. Exchange Server 2010 users access their mailboxes through the ISA server by using Microsoft Outlook Web App (OWA) together with Windows Internet Explorer. However, the users cannot open certain attachments. Additionally, the following error is generated:
If the users directly access the Exchange Server 2010 CAS server by using OWA, they can open these attachments.
Note The file types that are affected include .doc, .pdf, and .xls.

Exchange Server 2010 OWA adds a "Content-Encoding: none" string to a response and ISA 2006 SP1 adds a �Vary: Accept-Encoding" string to the response. The combination of the string in the response prevents Internet Explorer from caching the files.. Therefore, Exchange Server 2010 users cannot open the attachments by using OWA.

To resolve this problem, install the following update rollup:

For more information about headers for the Vary field, visit the following Microsoft Web site: