Hi,
The reason you can't see the attribute you created is because you created it on the "Support Group" object which is a child of the "Group" object. The "Create Group" relationship on the Resolution is a link to the "Group" object so you can only see attributes from that object level. If you delete the Boolean and then re-create it on the "Group" object you'll be able to use it in your existing calculation.
Thanks
Stu