Recently I've been getting this error message from mpeg streamclip. I have FCP 7 and I can see the AppleProResCodec.component in my QT library. When I attempt to export as a quicktime and choose the prores compressor I get this message - Error : can't open the compressor.
I've tried deleting completely mpg streamclip and re-installing, and I've downloaded a new prores component and replaced my local version. I've done a disk permission repair. Yet I still get this error. I do not get any problems when exporting from QT with prores.