This problem occurs if the following conditions are true:
- The following rules are configured in ISA Server 2004 or ISA Server 2006:
- A Content Type rule that applies to HTTP traffic is configured. This Content Type rule is evaluated when the POST request is processed.
- An access rule that enables the POST request to be submitted to the Web server is configured. This access rule requires the client to authenticate.
- The client sends the POST request to ISA Server over an unauthenticated TCP connection.
- The POST request that the client makes is an HTTP 1.1 request.
- The Web server sends back an "HTTP 100 Continue" response before it sends the "HTTP 200" response together with the response data.
In this scenario, ISA Server relays the Web server's "HTTP 100 Continue" response to the client as expected. However, ISA Server incorrectly does not send the "HTTP 407 Proxy Authentication Required" request to the client.