Clean re-install (after OS re-setup) did not help. Could it be resolution? I am on 1900x1200 on a big screen, so that may be a trigger... Testing the screen-resolution thingamajigg.
Playback will only go as far as 1280x1024. Anything higher than that will get into the error. It cost me a lot of time to go about checking the resolution, expecting the error to point to the right source of the problem. But no. It is clearly that the resource-file for handling the resolution for the main console is different from that for the Playback!
Mind you, it could also be the 4:3 screen-ratio, but 1600x1200 killed it too, so I'm not sure about that.
Now we need to get an update to have the correct resource-files for higher screen-resolutions. I also got the remote live viewer to look at all cameras, but only one at a time ('connect all' does not do squat, but disconnect one, and connect another one will show that one in pane #1).
Another one: The web interface for Playback works -more or less-, but the web interface for live viewer will not work. And playback only on IE8 32bit mode (Firefox or IE8 in 64-bit mode will not or only half work).