Domain mapping and IIS 6

Hello!
I've got a little issue with setting up domain mapping in combination with IIS 6. I purchased and downloaded the Domain Mapping plugin, installed it (that seems to work), and tried to set-up mapping.

I also set up the A record to the webservers IP adres.

But when I try to connect, I do not get a "redirect/mapping" to the desired site in my wordpress network, but I get a IIS login box (which states that no website has been found).

Does anyone has some tips?