I can't make any of the several ways of switching takes work, such as pressing T, shift/T , Choose active etc. I don't use this often but I remember that the last time all of the above worked. Next Take and Previous Take are also ghosted. Is there a setting somewhere that I should be aware of?

Have you added any takes in the first place? If so, the clip should have an n/n indicator.

Yes, I have placed one clip over another; both audio and video. When I go to Select Active, I see only one of these, the top one listed and a listing "None", even though there are two takes present.

What's an n/n?

I have it figured out; I forgot about the last step: "From the shortcut menu select add as takes." Now I know what n/n is (#/#). Thanks