2005 A4 Covertible Roof Problem

[mwg123]

I have a 2005 05 2.5 TDI Convertible. The roof has been working fine up until today. I put it down this morning and it just would not go back up. The warning on the dash is 2roof cannot be used" This isn't me being stupid im sure and the book sujests and fault. Are there any common ones? I have manually lifted and droped it to see if it may free something up but is has not. Any help would be greatly received.

Matt