(July 19 - I think that I have found the problem (and my solution) - see below)
I am using Sonar 4PE. This happens intermittently, not all of the time.
The GPO-Kontakt screen is usually minimized, unless an adjustment is to be made. Same with the Ambience reverb. They get minimized to the lower left corner of the screen (but the minimized 'box' is still visible).
From 3 different day's work (and about 7 or 8 - out of about 30 total - files that I am converting from another sampler to GPO), when I Open one of these files, the GPO and Ambience boxes have disappeared - not under the main screen, like my Console View is apt to do.
(3 hours later: I forgot to mention: The Synth Rack box does not appear when you select it, when the minimized GPO box has disappeared. Also, everything plays OK. You just can't make any adjustments).
Where did they go, and how can I get them back to the screen?
(I have been having problems being able to Reply and Post on this Forum, so please do not assume that if I don't reply, I am not interested. I am fully functional about 1 in 20 attempts).