I learned last year, through a painful few weeks that progressive updates of OSX not only removed my CUDA render engine, but updated OpenCL. With each update, Premiere CS6 became less and less stable, to the point of being useless (crashing the moment I scrubbed on the Project time-line).
I reinstalled the latest version of CUDA, switched all current projects to the CUDA render engine, and Premiere immediately stabilized with few problems since.
However, last night I installed the Premiere CS6 upgrades and this morning Premiere returned to a dismal state of dysfunction. Useless.
After two hours of deleting render files and user preferences thinking I had corrupt files, I checked the render engine settings. Seems the CS6 update reset my system back to OpenCL. Once CUDA was reset as the render engine, Premiere stabilized again.
A helpful warning to others who may be suffering the same frustrating state of total malfunction -- download the latest CUDA and avoid OpenCL.