The commands APPLY TO SELECTION , ARRAY TO SELECTION and DELETE SELECTION can create a set named LockedSet when used in a multi-processing environment. This occurs when a modification must be done on a selection while records that belong to this selection are locked by other processes. In this case, LockedSet will contain the records that the command has not been able to handle. Do not forget that the set will not be created automatically.
It's always a good idea to check this set after using these commands. To be sure that the set contains locked records, you can use the Record in set command to check if the set contains records or not. If no records were locked or if the set does not exist, Records in set("LockedSet") will return 0.