Two things that you can check for this problem. First check your /var/tmp and look for file like sim_rep1.sh~ or ~sim_rep1.sh and try to delete it. If the same problem keep occuring try to check your HDD Swap space. What is your hdd swap space that you reserve during your Unix installation ? Also one more thing, does your shell script that you are running needs direct access to Swap space ? Or does it require direct call of a Program structure ? Check either one of them. The most similiar that your problem might occur due to Solution number two that i provide. HDD Swap space. Try to check it out. Do return post.