The request failed with HTTP status 401: Unauthorized by mivchik

RSReportServer.config file stores settings that are used by Report Manager, the Report Server Web service, and background processing.
This file contains Autentification area which specifies one or more authentication types accepted by the report server.
Some our reports need access to external data sources with credentials of user who runs the report, so we need Kerberos authentication - RSWindowsKerberos .
We modified Autentification area in RSReportServer.config file

<Authentication>
     <AuthenticationTypes>
         <RSWindowsKerberos/>
         <RSWindowsNTLM/>
     </AuthenticationTypes>
     <EnableAuthPersistence>true</EnableAuthPersistence>
</Authentication>

When administrator opens report manager site he gets message “The request failed with HTTP status 401: Unauthorized”.
The same behavior is noticed with only <RSWindowsKerberos/> parameter without RSWindowsNTLM.

With <RSWindowsNegotiate/> parameter administrator gets enter login\password window and after entering them he is prompted again for them.

With only <RSWindowsNTLM/> everything works fine:
<Authentication>
     <AuthenticationTypes>
         <RSWindowsNTLM/>
     </AuthenticationTypes>
     <EnableAuthPersistence>true</EnableAuthPersistence>
</Authentication>

In the same network Domain is situated Reporting Server 2005. It works fine with Kerberos and allows double-hop authentication to external data sources.