The *ddl*lck* files are created by poster to insure that only a single poster instance applies a DDL that may have been broadcast to multiple poster queues. These "lock" filenames are constructed with the sequence number and offset of the redo record [from the source]; poster is supposed to clean them up periodically. Once again: these files are created quite deliberately, and not as a result of an error. Poster cleans [removes] them periodically.