Some audio files occasionally display as a flat line. This issue was specific to M4a audio files, and included some files from iTunes.
M4a audio files work initially, but at some point when opening the show the audio will stop working or display as a flat line. Once this happens, even when removing and importing the file the issue remains. This issue typically occurs after applying a update from the Devices, YouTube or Vimeo dialogs. This issue was first reported with ProShow 4.51.3003, and has been fixed in later versions.
The problem has been fixed by an update.
You can get this update in either of two ways: