This turned out to be a Microsuck problem. It may have been the server update that caused it, but the disk which ProSeries was installed on was set to write protected.  I didn't do that, Microsuck did it without my knowledge or permission. I had to run Dispart on the server and manually clear the readonly attribute. ProSeries now works as before, but I wonder how often I'm going to have to run the Diskpart utility if MS keeps setting the attribute to read only