Ours is run from cron. Perhaps you aren't closing down the application being dumped? In our case (obviously) it's an Oracle application, and this is shut down before the dump is taken, thus there is no chance that the device on which the Oracle database resides might be busy. Is this the case with you? If not, can you post the exact error message you're getting? Perhaps you could also post the script (suitably amended for privacy) you're using.