When taking a screenshot, there is a gray image displayed.
Before upgrading to Ubuntu 13.04 the screenshot was working properly, however, after the upgrading process the screenshot wont work no more. I tried to verify which package was the problem from: gnome-screenshot, I unistalled it and installed back on my laptop, but it wont work anyways.
shutter
viasudo apt-get install shutter
. It's a pretty decent screenshot tool, and it might not be worth spending time trying to fix gnome-screenshot.