I found the answer myself in the MSN webtool blog:
"
Easier Authentication
For the past year, we have heard from webmasters that authenticating their sites was a difficult and sometimes limiting process. For large site owners or those with many domains, it can be hard to manage all the authorization codes for your sites. In this update, we have simplified the authentication process by allowing you to use one authentication code for all your sites. In addition, you no longer need to specify between XML or HTML authentication methods for each registered site. You need only to add an authentication code to the site and we will check for both methods automatically."
Good blog, it was helpful to read. Probably more people should glance through the blog before submitting questions here.
Merry Chrismas!
