I coudn't launch PPCC at all. I always got the dreaded windows message Premiere Pro has stopped working.
After a huge amount of research, and a lot of much-appreciated interest and suggestions from many people, I've solved the problem by trial and error, without having to spend a penny on a new GPU.
I go into device manager, disable the GPU (ATI Radeon HD 2900 XT), launch PPCC successfuly now, and then enable the GPU. Hey presto! It works perfectly! (Does this imply that there is something not quite right in the PPCC launch program?)
I am sooo happy that the solution is so easy, and that it cost me nothing.