I think the cause of the freeze is what's explained in the caveats to using event structures in the on-line help. To quote:
"National Instruments recommends that you place only one Event structure in a loop. When an event occurs in this configuration, the Event structure handles the event, the loop reiterates, and the Event structure waits for the next event to occur. If you place two Event structures in a single loop, the loop cannot reiterate until both Event structures handle an event. If you have enabled front panel locking for the Event structures, the user interface of the VI can become unresponsive depending on how the user interacts with the front panel." There are other details in the help listing including a deadlock condition caused by a double-click.
