look up ulimit in UNIX using your DataStage userid and see what the limits are; you can also search this forum using ulimit to get a number of posts along a similar vein. You might have a soft or a hard limit on file sizes, this is the most likely cause as DataStage Px and Server limits on file output depend mainly on those restrictions imposed by the OS.
you are welcome - but could you post what the problem really turned out to be and how you solved it? That will make the search functionality work much better for anyone with the same or a similar problem.