Something really strange with the cookies

[ZedPain]

i have a problem with my forum cookies...

if i enter to the forum from this url
without the www

http://mydomain.com [nofollow]

im in my user..i can logout, and all working fine
but if im enter from this url with the www

http://www.mydomain.com [nofollow]

i need to login in to the forum...
the login cookies saving to only one url.. and the both urls are the same...

what can i do about it?

[flapjack]

you need to set up a 301 redirection for one of those addresses.
http://www.webconfs.com/how-to-redirect-a-webpage.php