You are seeing the double hop issue. This is not specific to RS but is an
issue when you have a user -> website ->another website. To implement this
configuration you need to be using Kerberos. I can't get specific to this
because I have not had to deal with it. Hopefully this gets you in the right
direction.

Signature
Bruce Loehle-Conger
MVP SQL Server Reporting Services
> For a SSRS 2005 report that is using SQL authentication which works
> correctly. However when called from another web server as a .Net
[quoted text clipped - 9 lines]
> What settings do I need to change to get the report to run from a
> ASP.Net web page?