Report Server URL- Authentication popup

Hi,

We do have a strange issue with the report server with Windows authentication enabled. (SSRS 2008 R2, hosted in Windows 2008 server).

The report server url opens for me in my local PC (Windows xp machine) and from another Virtual server running in Windows 2003 server. If we try access it from another windows 2008 server, the authentication window was been popup  and request user id/ password. Even though we supply it, it keep on request the same. we did not have the clue on this issue. Please assist us if you were aware of this.

Thanks, Jey