E51 Inner sun cover on rear sunroof won't slide!?

Hi all,
The deed is done and now I'm a proud owner of an Elgrand. Everything is fine except one little niggle. This is the minor problem of the inner rear sun shade won't slide back independently. It goes back with the sunroof and I've tried pushing it back when its on tilt. it slides back about an inch then stoops against something. I don't really want to start ripping headliners off. Cheers