One of my X2 projects has suddenly developed this thing where the screen only updates really slowly, even when the project isn't playing the aim assist cursor only jerks around the screen and scrolling up and down through the tracks takes forever. I've tried pressing pause/break to toggle cpu conservation mode and it hasn't made any difference. Pretty stumped over this, I tried clearing my hard drive and putting the project on a special partition on the fastest part of the disk with plenty of space but no dice.
 
Any ideas? Other tracks on the hd open fine, and although a bit sluggish on playback when those projects aren't playing the aim assist cursor updates fine and I can scroll up and down normally.

I've lost a day to this :( I suppose at least it forced me to tidy my hard drive a bit.

2 things to check:
 

1. Have you pressed the PAUSE key inadvertently?
2. Have you cleared out your picture cache recently? If not, do so.