A client computer may receive an error message when an ISA Server 2006 access rule limits access by content type: "HTTP 502 Proxy Error"

In Microsoft Internet Security and Acceleration (ISA) Server 2006, you can configure an access rule to limit access by content type. In this configuration, ISA Server may deny client requests when the response from the Web server has an entity body but does not include a "Content-Type" header. In this situation, a client computer may receive an error message that resembles the following:The client computer receives this message even when the content type is valid.

Typically, this problem occurs when a Web server returns an "HTTP 302" response to the ISA Server computer.

RFC 2616 describes the HTTP/1.1 protocol. According to this document, any HTTP/1.1 message that includes an entity body must include a "Content-Type" header field that defines the entity body's media type.

Some Web servers use "chunked" transfer-encoding to send HTTP response data, and the response may include only a zero-sized chunk in the entity body. Therefore, the entity body in the response has no data.

To resolve this problem, install the April 19, 2007 hotfix package for ISA Server 2006. For more information about this hotfix package, click the following article number to view the article in the Microsoft Knowledge Base: After the hotfix package is applied, traffic is enabled even if an entity body includes only a zero-sized chunk.

Microsoft has confirmed that this is a problem in Microsoft Internet Security and Acceleration Server 2006.

To view RFC 2616, visit the following Internet Society Web site: