OK, so the SoundCloud embed feature is pretty crap. You need to go to the SoundCloud page, then click Share, then click Embed and then you have to find the src= part of the embed code, and just post that, see example url below:-
Like this without the spaces around the :
https : //w.soundcloud.com/player/?url=https : //api.soundcloud.com/tracks/204001280
Scrap that, I found a regex and added it to the AutoEmbedMediaPro script and it seems to work OK now with the normal soundcloud links.