Recently, a fellow Mepis 12 user had problems with a computer. Some of the desktop effects stopped working after an unknown update. Thus, I had to try all I knew to fix the problem:
1. su -c 'update-alternatives --config libGL.so.1'
and chose #1 in the nvidia/diversions.
I also ran
su -c 'update-alternatives --config libglx.so'
and chose #1. But that had no effect.
2. su -c 'cd /usr/lib/xorg/modules/extensions;ln -sf $(ls -1 libglx.so.*) libglx.so'
and then restarted the x session.
...It didn't work.
3. I tried to see if there was anything blacklisted in the file
...But there was nothing blacklisted there.
4. Dedoimedo had this easy tutorial:
Basically, it tells you to move the file kwinrc located here: .kde/share/config/kwinrc
If you do, next time you start X, a new file will be created.
I tried it...but it didn't work, either.
5. Then, I read that for some Arch Linux users, that solution was pretty extreme. According to one of them, all you have to do is opening kwinrc to look for this line:
And set it to: OpenGLIsUnsafe=false
But it turned out that the line was already set to false in the file.
6. Finally, I tried something of my own. I noticed that kwinrc on the damaged system was missing the line:
Thus, I asked the owner to add it, just to see what happened.
Who'd have thought! It worked! :P Now the system's effects are working again!
This is what I love of Linux. You can solve problems if you are willing to learn and try. You are not denied access to your system.