I think I found the problem. The GConf key system->gstreamer->0.10->default->videosink was empty. I set it to "autovideosink" and gstreamer-properties works again!
I think I found the problem. The GConf key system- >gstreamer- >0.10-> default- >videosink was empty. I set it to "autovideosink" and gstreamer- properties works again!