Funny.....i just had that problem fixed on my car. My car got broke into and the driver side window busted in. I got a glass company to fix the window and put it in. Well a day later after it being fixed it came off the tracks. They came back and put some black coating stuff on it. Next day when i tried, it came off tracks. They came back and tried something else. Came off again. Finally on the third try, they had to put small metal strips on the tracks and clips off window to keep it on. That may be your solution if what the other guy said doesn't work. I wouldn't try doing it yourself, I'd hire someone to do it. Shouldn't cost too much at all. Just try and see.

~Green Civic EX