Report Manager 2008 r2 - prompts for username/password & does not accept

Hi all,

I am dealing with an extremely frustrating problem with Reporting Services 2008 r2, Report Manager, and would greatly appreciate any help.

I have installed Reporting Services, with Report Manager, onto a Windows Server 2008 r2 install. 

When loading Report Manager (http://server/reports), I get prompted for a username/password.

No matter what I type in, I get prompted a 2nd time, then a 3rd time, then a blank screen loads up.

@#$@#??!?!!

How can I get past this username/password challenge - remember this is SQL 2008 r2 so IIS-based solutions are not relevant.

Thanks again,

Jason