a Negotiate WWW-Authorization header (known as Pre-Authentication)ĭisabling Kernel Mode Authentication may cause web applications that require Kerberos authentication and delegation to fail.a Windows Challenge/Response (NTLM) header.The 401.1 response will occur if the web browser's first request that's sent to the IIS application contains one of the following headers: Or, the HTTP 401.1 error message may be displayed in the browser window. The web browser may prompt you to enter your username and password. In this scenario, IIS may return an HyperText Transfer Protocol (HTTP) 401.1 response to Internet Explorer in response to the browser's request. Additionally, this web request being sent by Internet Explorer is the first request to be sent to the IIS application.The Internet Explorer browser is configured to use Pre-Authentication, and Kernel Mode Authentication is enabled in IIS.You use Windows Internet Explorer to browse to a web application hosted on IIS 7.0 or higher.Original product version: Internet Information Services 8.0, Internet Explorer 10, 9 Original KB number: 2749007 Symptoms It occurs when you use Internet Explorer to browser to a web application hosted on Internet Information Services (IIS).

This article resolves the problem where an unexpected 401.1 status is returned with Pre-Authentication headers.