Inactive Batch Ticket Printing Sets

We've had a weird issue come up with our batch ticket printing sets:  suddenly a large number of them have become inactive.

www.tessituranetwork.com/.../Batch Ticket Printing.htm

There is a "Active Only" checkbox at the bottom of the listing of sets (unmentioned or shown in the documentation), but otherwise I see no mechanism to inactivate a set or difference in any parameter between the active an inactive sets.  Does anyone know what might be going on, and how to control if a printing set is active?

Thanks,

Gawain