I rebooted the system. Still have problems.

Well, you can double check and see if there are any stale lock files in the locks directory. If you're exhausting your system resources as Chuq points out, and your Python processes are either hanging, thrashing with other processes, or just getting waxed by your kernel, the processes holding the locks will fail hard, leaving stale locks around.

Yea - 28 files in the locks directory. Do I delete the locks?

Thanks for your help. I'll fix it in the morning.