Long story short, the culprit was SmartSound QuickTracks. When removed, the project - which contained several QuickTracks - re-opened just fine.
Figuring that the problem might be the result of a corrupted interaction between PPro and the Quicktracks engine, I uninstalled the QuickTracks plug-in. Problem solved. The project loaded just fine.
Community content is available under CC-BY-SA unless otherwise noted.