Audi Cabriolet 97 model: Problems with soft top roof

Hi There,
I have a 97 audi cabriolet, and have recently been experiencing problems
whereby the roof folding mechanism seems to jam mid way between the roof
being closed and open. It sounds like it is trying to lift the back flap,
but just cannot push it up. I was wondering whether anyone has had a
similiar problem, and what the cause of the problem may be. I have checked
the hydraulic fluid levels, and all appears to fine.

Any help would be appreciated.
Thanks,
Graeme