Addon Domain only without "www"

[atreiu]

I seen that my Addon domain that I registered, works only if I don't put the "www" behind it :

If I go to http://atretech.net/ It works fine.
But if I go to http://www.atretech.net/ it redirects me to http://www.atretech.net/cgi-sys/defaultwebpage.cgi

Did I done anything wrong ? I flushed DNS but no way.

Thank you.