Re: Hypersnap 8.11.02 - New issue with black screen when capturing
It could be still some Internet Security product, only smarter than seen previously. It may kick in blocking screen captures if a web page is on top, and it may even looks and try to guess if this is a generic web page that will not contain any private data (such as e.g. Wikipedia page), or something with personal data (maybe online banking or even Facebook?) I'm just speculating, but you could try to find a pattern when the capture is blocked, to see what was on the screen.
Again, one can usually enter settings of such Internet security program and tell it which screen captures programs are safe and should not be blocked.