Playback sounds "doubled" on one song

[Stephangus]

Hey folks. Having an issue with one song only: Regardless of whether effects are on/off, the playback sounds doubled; project wide and on individual tracks. This just started happening when I opened this song last week. I may have hit some global setting, or something. Any ideas? Thanks. -S

[Stephangus]

FWIW, I just imported a new file/track and it plays back fine in the same project.

[Stephangus]

Aaaaaaaand now it's all fubar'd. Happened on it's own about 2 hrs into todays session. Playback sounds doubled. I did nothing but hit the space bar and it started doing this. Hesitant to save and close...

[Stephangus]

Problem solved. New plugin going nuts.