Windows Login box appears while accessing certain resources

[Guest]

Hi,

I'm using Forms authentication in my ASP.NET web application. When I deploy
this application in a Windows 2000 server machine and access the application
.... everything works fine except that for certain resources like images
created using, excel exports a Windows login prompt appears. Now as a
temporary fix, I've created a local user in the server and we give the
credentials of this user when the login prompt appears.

For Info,

I've enabled Anonymous authentication in IIS. Also, I've set proper
privileges to ASPNET local user for all the necessary folders.
Thanks for any insight into why this is happening and how to avoid such
prompts.