Once again, old combinations, which NEVER should be changed, are broken, like recently with the O & F keys for the picture viewer. I want to use the insert key, as always, to mark the images. 
So, how exactly do i get it back, please. There are too many hits in the F1 manual, so maybe you can tell me which command it is, i can mark those images with. It is not a good idea to make "M" the selecting key, which, by the way, doesn't even work here.
Insert is still the default key for that (as well as M), that hasn't changed at all in Opus 12.
All the viewer commands are listed on the one page (the one for the Show command) and the first hit for "mark" on that page is the one you want.
Additionally, you can see what commands existing hotkeys run from Settings / Customize / Keys.
Ok, thanks, i will have a look. Just couldn't find it quickly. What do you think about adding a info tip into the image viewers context menu to the commands, to view the current commands?
You can view all the current commands from Settings / Customize / Keys.
Yes, i know. Sorry. Somehow i must have managed to erase a bunch of the old commands for the image viewer. I will check some older backup then
If you delete the file /dopusdata/ConfigFiles/viewer_hotkeys.oxc and restart Opus it will restore the default viewer hotkeys. We'll add an easier way to reset the default keys in the future.
Ok, i will give that a try. & a good idea.