cannot re-fit windscreen with new rubber using rope it keeps jumping off bottom when pulling rope up sides

w smith in fife scotland, July 2013

It is difficult to know what is going wrong,have seen these done by windscreen replacement co`s and they make it look easy,working equally along the bottom,up the sides and finishing along the top,are you using some lubricant to help?maybe a small amount of soapy water,also I take it the centre bead is removed while doing this.

cdc, July 2013