While I don't know what is causing the problem, if in the event that you are using fedora, or something similar, gstreamer is ususally the main, so try this on your terminal:
su to root
enter the following: gst-register
if the file is not found, and you are up todate, then enter instead the silly things full name (because of the update):
and press enter. This will reload and find and whatelse all of the plugins.
Hope this works for you.