url with www prefix not authenticated in asp.net membership

Hi,

I am using asp.net membership in my website. the problem is that pages with 'www' prefix is not authenticated and forces the user to the login page.

for example the following URL takes the user to the profile page:

http://site.com/EM/EmProfile.aspx

but the http://www.ir-translate.com/EM/EmProfile.aspx URL redirect the user to the login page:

http://www.site.com/Login.aspx?ReturnUrl=%2fEM%2fEmProfile.aspx

How can I overcome this?

Thanks and regards