I got the same notification when trying to activate blur, I think the reason could be due to the graphics card my machine is using. When I checked kwinrc in ~/.kde4/share/config/kwinrc I found this;
Advanced Micro Devices=DRI R600:-:7.8.1,DRI R600:-:7.8.2
Ati=Radeon HD 3650:-:3.3.9901
my guess is that if your graphics card is blacklisted, blur won't work.