Right I am guessing this is what you did…
In the Domino administrator files tab .
Right Click > Cluster > In Server (sort of what you said above).
<b>From Domino Admin</b>
If you’ve marked a database “out of service” and now want to <i>restore access to the database</i>, you must mark the database “in service.” When you put an out-of-service database back into service, it becomes fully available to users.
1. In the Server pane of the Domino Administrator or the Web Administrator, expand All Servers or expand Clusters.
2. Select the server that contains the database you want to mark “in service.”
3. Click the Files tab.
4. Do one of the following:
In the Task pane in the Domino Administrator or the Web Administrator, select the folder or view that contains the database you want.
In the Task pane in the Domino Administrator only, expand Cluster Directory (6), and then select the view you want.
5. In the Results pane, select the database or databases you want.
6. In the Tools pane, expand Database, and then click Cluster.
7. Click “In service,” and then click OK.
Basically if you want to stop people access the database in a cluster (<—- important) you mark it out of server. This is done to stop the cluster tasks effecting FIXUP or other maintenance tasks.
I hope this explains why.