When returning to PDC from other software, like returning from ISL, PDC tries to verify that all the slave processors are in the expected state (i.e. that all slave processors are asleep); however, this event ID indicates that at least one processor active in the partition was not asleep. So, PDC is going to reset the partition. The data field of this Event ID is the global CPU number of the first CPU in the partition not found in the expected state.