I modified Mark's to make it much less difficult so I didn't feel as bad.

Anyway, I thought that the 22 other people who didn't solve it might want to try my version too, so here it is!
All credit goes to Mark for making a brilliant (and difficult) level, you might want to play it before you play this one! http://pcpuzzle.com/forum/viewtopic.php?t=26534
Difficulty Rating: cloud+
Video solution