Error when attempting to access Reports: "Unhandled system exception: The request failed with HTTP status 401: Unauthorized"
This was an error which typically occurred prior to HEAT 2014.1.1.
If you are receiving the error in 2014.1.1 or later (or if in earlier versions, after applying the fix below) the problem is a conflict of the actual authentication used. The account that is in use is the service account for the HEATAppServerAppPool application pool. This account needs to be able to authenticate with the SSRS instance (should be the SSRS service account), as well as a local admin on the app pool machine.
Prior to 2014.1.1, you will also need to remove the below entry under <AuthenticationTypes> in <SSRS_DIR>\Reporting Services\ReportServer\rsreportserver.config:
For example, SQL 2012 with a default instance would be C:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\ReportServer\rsreportserver.config
Then restart SSRS, as well as IIS on the application server.