Just a reminder--non-existent databases being referenced in a maintenance plan do not show up in the list of specific databases to backup, but they are still there. I had the plan set to backup specific databases, and ignore those that were offline. Today I detached a database that had been offline for a couple weeks. Not seeing it in the list of databases to backup threw me for a while. I reattached it, edited the maintenance plan by unchecking it in the list of specific databases, then detached it. Hope this helps someone else.