Replacing the 24VDC power supply with a larger output model seems to have fixed the "E-stop" error annoyance. I will never know if it was defective or just sized too conservative. The linear type power supplies are derated according to ambient temperature, and it was probably getting to 40 degrees centigrade (about 105 F) in the cabinet. Those power supplies have automatic thermal shutdown, which would automatically re-start (after the "E-stop" condition occurred) when it cooled sufficiently, that could occur very quickly in the case of a marginal overload. So I suspect that the PS was operating as designed by the PS manufacturer, but I would never install a used power supply in another customer's machine to find out. This machine is in Maine, USA; we do not have nearly the hottest summer temperatures in the country. And, my closing comment: I was not able to associate the failures with high daytime temperatures. I wish good luck to all of you.