I finally got everything working, despite the ineffectual help of the Adobe support team. Maybe my solution will be helpful.
I loaded a duplicate of my system saved BEFORE installing the Cloud Manager onto another drive. Then I loaded the Cloud Manager onto my current boot drive and sure enough, got the Error 16. Then I loaded the OLD version of the Adobe PCD file from my duplicate drive. No go. Then I loaded the OLD SLStore file. Still Error 16.
BUT then I replaced the SLCache folder and BINGO! problem gone. I noticed in the folder is another called SLConfigs. I am not sure it is a permissions issue or something that happens to this file when the Cloud Manager updates these files, but by reloading the pre-install version of this foldeer I have fixed the problem. I repeated the fix on another machine. I have now downloaded the CC apps with no issues.