Security problems with Silverlight 3 application

I have a Silverlight 3 Application and for security I'm using开发者_运维问答 Active Directory. For some reason that I can't explain whenever I access my app in the production servers the default browser authentication window pops up and I have to Authenticate two times!

Whats up with that? I checked IIS and everything seems fine!

As EricLaw said:

If your "production server" is using a FQDN (e.g. one with dots) then I'd expect at least one prompt because NTLM/Negotiate do not automatically authenticate in the Internet Zone

I had my WCF endpoint pointing to the servers Extranet address. I don't know how I missed that.