ReportViewer credentials prompting problem

Hi,

I have a similar problem to others posted here but cannot figure out what is
'wrong'.

The issue is that during the rendering of a remote report in the reportviewer
control the user is prompted for credentials for the server multiple times - it
appears once for each resource that is accessed via the report services web
service, i.e the images shown in the toolbar etc. The page that the reportviewer
is hosted in is fully visible.

If you cancel the dialog on each occurrence about 50% of the time the report
still displays correctly (minus the toolbar images) other times it never gets
the report stream and just show the 'report processing' text or whatever.

IIS 6.0, reporting services are all on the same Win2003 box.

App is running in its own pool with an identity using a domain account.
(Original idea was that then this account is the only account that needs access
to the reports etc)

The problem doesnt exist when I run the ASP.Net app from the VS version of IIS
and it doesnt happen when you access the page on the same machine as IIS.

The app does not allow anonymous access but its as though after making the
inital request to run the report the credentials are not passed for requests for
any of the resources.

I my frustration I have added a custom IReportServerCredentials class and tried
various options which all give the same result. I even added a label on a report
displaying the user running the report and this is always shown correctly
depending on how the custom class has supplied the credentails and the ASP.Net
impersonation settings etc.

If I hack my app to allow anonymous users access it works, (without the custom
IReportServerCredentials class the app pool identity is used to access
reportserver) but I need to prevent anonymous access.

It also works when deployed to my local XP IIS but only if I set that up to
impersonate a fixed user that has access to the reports.

Any ideas please?

Norm