This is an MVS message indicating that a duplicate catalog entry exists, e.g. if you already have a dataset with DSN = 'xxxx.yyyy'. and you try to create one with disp new, catalog. You would get this error. the program open and write would go through and at the end of the step the system would try to put it in the system catalog. at this point since an entry already exists the catalog would fail and give this message. You can fix the problem by deleting/uncataloging the first dataset and going to the volume where the new dataset exist (this info. is in the msglog of the job) and cataloging it.