Comment 11 for bug 1699898

I had the same issue (with TDE as desktop environment), and solved as follows,

Step 1. I purged gnome-screensaver (that was the only screen saver package installed
other than xscreensaver). This step alone wasn't enough.

Step 2. I rebooted. (Maybe restarting xserver would have been enough, but I didn't think
about it). Now caffeine works.

This is a bit strange because the screensaver running was the one from xscreensaver package,
so I don't see why purging gnome-screensaver should have any incidence, but it solved the problem for me.