I've got exactly the same issue - Game played fine for about 2 weeks after loading then stopped with the flicker and the black square, like its trying to start, but doesn't. Suggestions at other sites with same issue said it worked through GOG so I came here - didn't work here either. Disabled my network protection - still didn't work. Turned PC on and off - still didn't work. No idea what happened except it was working OK for a while ..................... and now it isn't in both platforms.
I'm in Windows 7 and other games play fine.
I attempted to buy Caesar III and it went exactly the same way which leads me to believe there is something in that specific series of Impression games that is now suddenly incompatible with something else and it wasn't before.

At the moment unable to work out what it is exactly by trouble shooting.

Hi all same here

It doesn't even open. I tired what was suggested above but nothing fixed it so far.

I am having the same issue - but I am playing on a Mac via PortingKit. Any ideas?

If anyone is still interested, I had somewhat similar issue on Windows 7. The game didn't start after selecting Play from Gog client or from desktop shortcut (althoug I didn't encounter any flickering screen). I checked the support and the first suggestion worked: run the game as administrator. Hope it help at least some of you.