Domain Mapping not working with www.

Hi There,

we are running a multisite with various mapped domains. Now we have a problem with a single site:

while gesundesessenfuerkinder.de is working well. http://www.gesundesessenfuerkinder.de is showing a white page. When you ping http://www.gesundesessenfuerkinder.de it shows the right server IP.

What can we do?

Thanks.