You cannot map an expression in a source table to a key column in a target table if the TARGET_KEY_CHG column of the IBMSNAP_SUBS_MEMBR table is "Y" for that target table. This means that when using the Replication Center to create a subscription-set member, you should not select the option Let the Apply program use before-image values to update target-key columns if a key column in the target table is mapped to an expression in the source table.