Whenever I try to access SSRS 2008 R2 through a URL (i.e. after being published on the net), it always shows a login prompt when accessing the report. The problem does not appea
I'd start with using Internet Explorer, on a domain.. which will pass your credentials (if that is how you have this configured).
It IS possible to configure firefox to pass Windows Authentication / Token.. I don't remember how I had done this previously.
The BEST platform for using SSRS is Apple / Safari.. because when you hit the checkbox that says 'remember password' it actually remembers the password. It blows my mind that Chrome, Firefox, IE give you a prompt that says 'remember password' - but from my experience, remembering passwords only work as I expect when I am using Safari.
Disable loopback
http://thetazblog.taznetworks.com/2006/03/crm-30-sbe-sql-reporting-error.html
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I am assuming the prompt is for the username / password for the domain. Internally you are likely getting through the AD authentication check in your application as you will have permissions to deliver the report (you can test that premise with Firefox or other browser that doesnt handle AD authentication like IE does/
I think you may have setup for basic authorisation to view the report RSReportServer.config rather than web.config is that what you have done? (see this to see example http://msdn.microsoft.com/en-us/library/cc281309.aspx.)
If you are trying to get full anonymous access then you are in for some fun; luckily one of the RS team blogged a way to achieve it; I wouldn't advocate doing it straight onto a production box though.
http://blogs.msdn.com/b/jameswu/archive/2008/07/15/anonymous-access-in-sql-rs-2008.aspx
I'm not sure from you're question is the login box a prompt to get you access to the report server or is it a prompt on the reports datasource.
It sounds a bit like permissions to access the report server, I guess you could try giving the app pool user permissions to access the report server and run the report or use an impersonation account to access the report.
I was running into this problem for a different reason than the accepted answer. While SSRS was installed, it wasn't properly configured. Being new to installing SSRS, I had assumed some tabs in the Reporting Services Configuration Manager were set to defaults. They weren't. Once I went back and actually set them, everything worked fine.