Cabriolet Roof

I have a 96 Audi Cabriolet that the roof has just stopped working... Basically, when I try to open the roof the roof canvas folds and then
the back parcel shelf which should lift to allow the roof to fold into only raises a couple of inches before giving up after a few seconds... I have seen some other people have had this problem and was wondering if anyone has any idea what the problem could be? Any advice would be massively appreciated... Cheers, Mark
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