Submitted by northben on Tue, 12/23/2008 - 16:38
If you have Reporting Services, SQL and IIS installed on the same server, you may receive an HTTP error 401 that says, "The request failed with HTTP status 401: Unauthorized." The solution is to "Disable the loopback check" using regedit. Instructions are found on Microsoft KB 896861.
Importantly, you may receive this error regardless of which computer you are using to browse the report website.
