This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
When you attempt to connect to a Web site through proxy server, the following error may appear:
HTTP/1.1 407 Proxy Authentication Required
You must authenticate with a proxy server before this request can be serviced. Please logon to your proxy server and then try again.
This error is returned when you try to access a Web site through a proxy server that has access control turned on while using Basic Authentication.
The Web Proxy, through a 407 HTTP response, requests credentials from the browser client (or downstream Proxy Server). The client provides the credentials, or in the case of a downstream Web proxy, the proxy server may provide the credentials itself.
If the credentials used by the client or by the downstream proxy server are not allowed by the upstream proxy server, this error will be displayed.
This can be resolved by passing the correct credentials to the proxy server. Contact the administrator of the proxy server and verify that the account has permission to use the proxy server.