MSSQL Server, error number: 2601

I setup transaction replication between sql 2000 (Publisher and local distributor) and sql 2005 (Subscriber).The db replication was running fine until I implemented a small change on Publisher server.exec sp_changearticle 'KM_Data', 't_table1', 'del_cmd', 'NONE'goI run the initial database snapshot and it was completed.Then, I got an error on:"Cannot insert duplicate key row in object'dbo.t_table2' with unique index 'aaa_t_table2_PK' (Source MSSQLServer, Error number: 2601)"Please help and advise.Thanks,TJ