Error importing audio files

I know this post is old but I was having the same issue today.  I use a Mac with Parallels.  Anyway I tried all the suggestions here and still couldn't get it to work.  After doing some troubleshooting and trial and errors I figured out that Storyline does not like subfolders, I had created a folder for my project, then within that folder I had sub-folders for my elements (images, audio, music, documents etc)  Anyway, I edited my audio files which were in the "Audio" folder, then I created a sub-folder under "Audio" for my edited files.  Before it gets more confusing this was my folder structure:   Project/Audio/Edited Audio/.  I moved my audio files out of the subfolders and just placed them in the Project folder, and that fixed it!  I hope it makes sense to you all.