the media item you uploaded could not be processed

[Alpha1]

I got this error here on xf.com
Unfortunately, the media item you uploaded named Kalimba.mp3 could not be processed. Please upload a different file and try again.

Yet, I am able to upload this file to my server. I have mp3 support for XF1 active on my site.
Why does it not work for XFMG here?
the media item you uploaded could not be processed

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