SiteMinder with Windows Authentication doesnot work outside from Domain

Hi ,

We have WCF service deployed in IIS7.5 and it is having configured as Windows Authentication and Annonymous in IIS and in Web.config.

And we have a silverlight application , which is  communicating with this service. This works fine when we are in Intranet or within our Domain.

Now , we also have SiteMinder agent which is there for Internet user to access the Service. Which doesnot work at all. Giving Internal server error alway.

I have verified the Http Request and Response , and both having SMSESSION cookies after the user is being authenticated from SiteMinder

Can somebody help me in troubleshoot this problem?

Do I need to change some settings in IIS ?

Or do I need to changes something in my code ?

Thanks-Bikash