Bridge CPG / PHPBB2 both on different subdomain

[bugattibuilder]

 have the following issue when trying to bridge coppermine and XXX:
[error message here]

Coppermine install: http://photo.bugattibuilder.com/
Forum install: http://forum.bugattibuilder.com/
Coppermine version: cpg1.4.9
Forum version: PHPBB2 2.0.21
Test user account: test / test

BridgeManager settings:
Forum URL:  http://forum.bugattibuilder.com
Relative path to your BBS's config file:  ../forum.bugattibuilder.com/ 
Use post-based groups?:  0 
Cookie prefix: phpbb2mysql

PHPBB2 cookie settings:
cookie domain: <empty field>
cookie name: phpbb2mysql
cookie path: /
cookie secure: 0

I am running Microsoft Windows 2003 with IIS 6 (Small Business Server).
The forum is installed in \websites\forum.bugattibuilder.com
The cpg is installed in \websites\photo.bugattibuilder.com
Both are standard installs, with no mods.
My provider changed the DNS records for bugattibuilder.com in such a way that both forum.bugattibuilder.com and photo.bugattibuilder.com are pointed to the same (my) IP address. I use http headers to separate the requests again in IIS.

Is it possible to bridge the installations?

I will try out some options within the next hour, and will post the outcome by editing the post.

Tried:
-Change cookie domain in PHPBB2 config to    .bugattibuilder.com   so it would be readable by CPG. However, this prevents me and the test user to log in to PHPBB2.
So changed it back again (with phpmyadmin). (empty field).

Tried:
a completely different approach: IIS can use "virtual directories" which are directory entries in the directory tree (of the website) which point to another directory somewhere on the harddisk. This way it is easy to gather and organise data in a web-tree, while the data can reside on different places on a hard drive.
I made a virtual directory in the "forum.bugattibuilder.com" website, named "photo". I pointed that to the "photo.bugattibuilder.com" website. Thus, the coppermine software is now not only reachable under http://photo.bugattibuilder.com" but also under http://forum.bugattibuilder.com/photo.
This might be something which can be useful solving the problem. Anyone an idea about this?

[Nibbler]

Cookie domain should be .bugattibuilder.com. Clear your cookies whenever you make changes to cookie settings.

[bugattibuilder]

I tried that, as it would be the most simple solution by far.

However, I have not been able to login again, neither at home (directly connected to server, adapted host file) or at work (regular situation).

Perhaps a DNS situation? (www.bugattibuilder.com has a different IP than forum.bugattibuilder.com. Very well possible that this might be an issue.)

----------------
At the moment, I have installed coppermine again on forum.bugattibuilder.com/photo, dropped the tables on the database and recreated everything again using the install script. For now, this works, incuding bridging, however, the situation is not optimal.
I am still interested in a solution.

After my holiday, I will talk to my provider, and dive into the DNS. I suspect the problem might be there.

[Nibbler]

It has nothing to do with DNS. When you have set the cookie domain to .bugattibuilder.com post here so we can see why you are not able to login.

[bugattibuilder]

I am at the point of leaving for holidays for 2,5 weeks. After that time, I will dive into this again. I will post in this thread when I am back. Thanks for reading and looking till so far.