Unlike the rest of IPB, which uses a maximal permissive mode (that is: if a member is part of two groups, and one group can see forum X and another group cannot, the member can see forum X), for the databases, IP.Content uses a minimal permissive mode (that is: if a member is part of two groups, and one group can access database X and another group cannot, the member cannot access database X).
I have had to open my databases to be editable by everyone in order to get volunteers to add content, instead of being able to specify a volunteer group that had the ability to do it.