This problem is solved. The solution was complex, and since several of the other threads having to do with this seemed unresolved, I'll give some details. I had an exceptionally positive Adobe Customer Service experience when I phoned for support, and worked with an excellent Adobe tech support specialist who was certain that this was a permissions issue. Unlike any of the other permissions that I have seen discussed, she changed several permissions, including the actual permissions to user/library/Preferences; that is, to the entire Preferences folder in the user library, not just the Adobe components. How this would have been changed, and apparently changed just since downloading the CS6 update I cannot guess, if in fact it was.
The Adobe Tech Support analyst (screen sharing) reset several other permissions to read and write, but this was the very mysterious one for others to be aware of. In the Get Info / Permissions pane, at first the actual user account (there is only one on this machine) and the admin were not visible. She added them using the plus button in that pane. Once visible, they could not be changed, a mystery which is still not solved. She said (correctly) that that problem was not something related to the Adobe software but to this machine, and that Apple should be able to help. The final mystery is that when I phoned Apple a few hours later, both permissions (user account and system) could now be modified.
Once the permission for the user/library/preferences folder was set to read and write for the user account I was using, the problem was completely solved. I cannot be sure that it was not also partly solved by some of the other permissions that the Tech Support Specialist had changed for me.
Thanks very much, and Thank You to Adobe Technical Support!!