Window Track Problems

["Cary Henry" <caryhenry@hotmail.com>]

I just started having a problem with my driver's side window.  When I roll 
the window down, it will move toward the rear of the car and fall out of the 
front track.  This obviously causes a jam, and I must reposition the front 
of the window in the front track.  What is causing this, and how can I fix 
it?

Thanks,
Cary