This problem occurs when you try to import an audio to camtasia and gives you the error NO CODEC AVAILABLE TO RENDER THIS FILE.
I have tried downloading different kinds of codecs but none worked for me. so here it is.
The trick is converting your your audio file to mp3..i know some of your file is already mp3 but trust me this works.
download TOTAL AUDIO CONVERTER http://fileml.com/2g968b
instructions are already included in the file and it is already crack.
your good to go