We had this problem and solved it.
We have successfully exported a surround project in WAV and WMV formats.
Set up a surround project
File/Export/Audio Mixdown/File format/Windows Media Audio File then Codec Settings/ General: 44.100 kHz, 16 bit, 5.1 channel, / Encoding Scheme: Constant Bitrate, 440 kbps, 44kHz, 5.1 channel 16bit CBR/OK.
Export : error message: NS_E_AUDIO_NOT_INSTALLED/ press OK
Audio mixdown dialog opens again. Press Export.
Dialog box opens: File exists already! /Create Unique Name.
Then everything works!
So it appears the error message: NS_E_AUDIO_NOT_INSTALLED/OK is a false alarm.
You just need to press the Export button twice!
This bug only seems to happen the first time you try to render the project. After that it works fine again and again.
Change the destination folder and the bug returns.
Good luck! 
Press Export again. Fixed!