Outlook Web Access Error Message "Internal Server Error" with Certain Firewalls

When you use Microsoft Internet Explorer 5 or later to gain access to Microsoft Outlook Web Access (OWA), you may receive the following error message: However, OWA works when you use a virtual private network (VPN) or a local intranet. Earlier version browsers also work.

This issue can occur because the Hypertext Transfer Protocol (HTTP) 1.1 is used when you use Internet Explorer 5 and later to gain access to OWA, and the HTTP 1.1 protocol is not supported by all firewalls. If the HTTP 1.1 protocol is not supported by the firewall, certain packets from the client are blocked and you receive the error message in the "Symptoms" section of this article.

To resolve this issue, implement a firewall solution that supports HTTP 1.1 packets.

To work around this issue, do one of the following:

• Implement a SSL connection so that no requests are filtered.
• Modify the firewall so that the firewall passes all HTTP packets regardless of the protocol
• Use an earlier version browser.

For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base: