Ok, so here's the latest: Playing the track, there was an audio dropout near the end. Just before that happened, the disk loading indicator flashed red, and it showed 97% or so disk loading. Then it stopped. So I checked for fragmentation--0%. Then I copied the project files from my J drive to my C drive and ran the tune from there and it ran fine (42% by the end). So you'd think it's a problem with the J drive, except there's been no problem 'til today, and it's having the same glitches (sluggish, slow scrolling, white screening during pastes, etc.) others are having, so....
Any way to go back to X3c?