I do not know how any of this might impact PrE users, but in the PrPro forum, one user encountered the complete loss of WAV playback in PrPro. He traced the issue to having installed JUST the updates for SmartSound's QuickTracks plug-in for Premiere, and NOT the full plug-in, plus updates. He catalogs his efforts to fix the WAV issues in this THREAD.
I'm posting this as a H/U, just in case someone has installed JUST the SmartSound QuickTracks updates, without the full plug-in and they loose the ability to play back WAV files.
Hope that this helps someone in the future.
Remember - this is directly related to PrPro, but might also play a role with PrE, especially earlier versions of the program, before QuickTracks for Premiere were added as part of the installation.