in the terminal you get a trace that you can read to see what the program is trying to do. I won't quote it here because I'm too lazy to reproduce it. However, it basically is saying that the gtk-window-decorator has caused a problem with the X server because it couldn't load the .xml file it pointed to during launch.
This is the case because, for some reason, the gtk-window-decorator is looking for an .xml file in ''/usr/share/them