Print-Screen button does nothing. I bound the keys to scrot as suggested by Vasa. That did not do anything, but scrot does work from the command prompt. So then I tried replacing lxsession-default as suggested by Joern. That did not do anything. I see at the end of the bug report they say the bug is fixed in 14.04. It is not for me ! Does anyone have any idea why this does not work ? As far as I can see the key needs to invoke a command in the appropriate environment. I can't see why this has been giving problems for so many years.
Sorry ... PrintScreen button is working fine. I made a silly mistake.
I was immersed in what I was doing on a headless machine through teamviewer. Teamviewer does not send the PrintScreen key to the remote machine. It is processed locally. I just found all the screen shots I tried to get (of the headless client screen !) on the host machine. To it's credit teamviewer is so good that I forgot that I was using a remote system !