When the reliability analysis(six sigma) using Abaqus and Isight is performed, the error message stated

abaqus command failed with exit code 1

is sometimes occurred during the iteration process of reliability analysis. If I run the Isight file again, this error is disappeared and then reliability analysis is completed clearly. Otherwise such error is happened again at different iteration number and the analysis work is stopped. When I look into the Runtime directory, I can't see any error messages because log, dat, inp and jnl files are not created at the iteration number having this error. I googled to figure out this problem, however, I have not found a perfect solution yet. Let me know how to solve this problem.