Yesterday I needed to install freeglut3, and ubuntu was saying that it needed libglu1-mesa=8.0.4-0ubuntu0.2 while 8.1~git1206081121.640409~gd~p was to be installed. So in order I did apt-get install --reinstall libglu1-mesa=8.0.4-0ubuntu0.2 and freeglut3 finally got installed. when I started ubuntu today, It got me onto Unity 2D. I got from that that what I did yesterday was not wise. Now compiz cannot start properly I suppose. I don't know if it is going to work, but if I install the version I had yesterday will it switch automatically ? Also, I do not know how to do it, installing the latest version of libglu1-mesa