Error scanning wma files / gstreamer plugin missing

According to codecs wiki i have tried

apt-get install gstreamer0.10-plugins-good
apt-get install gstreamer0.10-plugins-ugly
apt-get install gstreamer0.10-plugins-bad
apt-get install gstreamer0.10-plugins-base
apt-get install libxvidcore4
apt-get install gstreamer0.10-ffmpeg

but the newest version is already installed for each of the above.

Checking the installed codecs:

gst-inspect-0.10 |grep decode |grep wma
ffmpeg:  ffdec_wmapro: FFmpeg Windows Media Audio 9 Professional decoder
ffmpeg:  ffdec_wmav1: FFmpeg Windows Media Audio 1 decoder
ffmpeg:  ffdec_wmav2: FFmpeg Windows Media Audio 2 decoder
ffmpeg:  ffdec_wmavoice: FFmpeg Windows Media Audio Voice decoder

Looks like that the wma codecs are installed?

But trying to play a wma file stil results in an errror:

root@MusicBox:/#  gst-launch-0.10 filesrc location=/tmp/b.wma ! decodebin ! alsasink
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
Missing element: Windows Media Audio decoder
ERROR: from element /GstPipeline:pipeline0/GstDecodeBin:decodebin0/GstASFDemux:asfdemux0: Internal data stream error.

I have also tried

rm -f /home/mopidy/.gstreamer-0.10/registry.arm.bin

without any result.

Any hint on how to enable wma support would be very nice!