Question about domain/subdomain

[amigadude]

I've tried bridging coppermine with phpbb2 and I had trouble....

mainsite is http://www.fiestatime.amigadude.com
phpbb2 is http://forum.fiestatime.amigadude.com
coppermine is http://gallery.fiestatime.amigadude.com

all subdomains are hosted in the same directory

coppermine bridging is set to
Forum URL:      http://forum.fiestatime.amigadude.com
Relative path to your BBS's config file:    ../forum.fiestatime.amigadude.com/
Use post-based groups?:    0
Cookie prefix:    phpbb2mysql

bridging with it setup like that had the login in coppermine redirects you to http://forum.fiestatime.amigadude.com/login.php to login.  It didn't return you to coppermine after login and it hasn't logged into coppermine when I manually go to http://gallery.fiestatime.amigadude.com (haven't added a gallery link to the forum header yet)

I was kind of in a hurry so I just stuck it in a gallery directory on the forum subdomain and now it works fine with these settings:
Forum URL:      http://forum.fiestatime.amigadude.com
Relative path to your BBS's config file:    ../
Use post-based groups?:    0
Cookie prefix:    phpbb2mysql

But and here's the actually question... should it work with the forum & coppermine on 2 seperate subdomains (forum.domain.com & gallery.domain.com) or would 1 of them have to be on the domain (domain.com/forum&gallery.domain.com or forum.domain.com&domain.com/gallery)

and.... I've solved it myself.... You want to leave this here to stop others asking the same dumb question?

Solution:
in phpBB config set the cookie domain to the highest common subdomain (or just the domain) mine was: fiestatime.amigadude.com