Use
Locking a business event temporarily closes the attendee list. You can lock both internal and external business events in both planned and firmly booked status.
Unlocking a business event releases it for bookings again.
Prerequisites
For locking:
The business event may not be
For unlocking:
The business event may not be
Result
When you lock a business event, a lock flag is appended to the Business Event Info infotype (1026).
Locked business events no longer feature in the business event catalog. This means that no further bookings are possible on this business event.
When you unlock a business event, the lock flag is removed from the Business Event Info infotype (1026).
Unlocked business events are included again in the business event catalog, which means that it is possible to make bookings for them.

Unlike canceling, locking a business event is not final or irrevocable. The business event can be unlocked again.
See also:
Locking a Business Event Unlocking a Business Event