Tip for: 10.06.14
Are you adding new copies to your collection before the items are available? Set their status to In Processing.
There is a preference for this as well as an import setting.
To set the status for new copies for an individual import:
In version 7:
In version 6:
To make it so all new copies start with a status of In Processing:
When your new copies are ready to be circulated, bookdrop them, and their status will change to Available.