The plastic slide most likely broke. Mine has done this. You can spend the $ and order a new one or pull out the existing and make a new slide with a nylon washer for 50cents. You will have to press it on but it is not hard and mine has worked for over 2 years. It's not that bad of a job but be sure to grease the slide.
The link below has the procedures for the repair.
http://www.carolinarovers.org/Old%20.../tech_page.htm
KF
