Hi Andreas -
Thanks for your message and sorry about the problems!
Did you move / delete the audio samples from the folders inside the application's document directory? Every scene copies its required files to a directory with the name Scene_[yourscenname]. There is a .plist file inside that directory that describes the scene, so if files get moved / deleted, the scene will fail to load. I will work on making the error handling a little more robust for future versions.
For now, the best way to delete scenes is to swipe left on the scene's row in the browser inside the app. This will bring up a delete button on the right side of the row (just like deleting an email on the iPhone). Alternatively, if that doesn't work, use filesharing via iTunes, select the Scene folder you want to delete, and delete it using the delete key. More info on using file sharing here:
Hope this helps!
Thanks,
Chris