ORA-23412: master table's primary key columns have changed

On Snapshot DB  - try I:
DROP MATERIALIZED VIEW GSM_SERVICE_MERGED_NETWORKS_SS
CREATE MATERIALIZED VIEW GSM_SERVICE_MERGED_NETWORKS_SS
REFRESH FAST ON DEMAND
NEXT NULL
AS
SELECT merge_network_id, item_id, active_ind
FROM GSM_SERVICE_MERGED_NETWORKS@TONPPROV;

CREATE MATERIALIZED VIEW GSM_SERVICE_MERGED_NETWORKS_SS
*
ERROR at line 1:
ORA-23412: master table's primary key columns have changed


On Master DB:
DROP MATERIALIZED VIEW LOG ON GSM_SERVICE_MERGED_NETWORKS; 
CREATE MATERIALIZED VIEW LOG ON GSM_SERVICE_MERGED_NETWORKS TABLESPACE IGT_TABLE;

On Snapshot DB - try II:
CREATE MATERIALIZED VIEW GSM_SERVICE_MERGED_NETWORKS_SS
REFRESH FAST ON DEMAND
NEXT NULL
AS
SELECT merge_network_id, item_id, active_ind
FROM GSM_SERVICE_MERGED_NETWORKS@TONPPROV;

Done