Request for help: Manfrotto tripod loose centre column (1 Viewer)

Hi everyone.
I've got a Manfrotto 190CX3 tripod which I've had for about 6 years and which has served me very well. However, last week the centre column suddenly became loose. Basically the bolt at the top of the legs no longer tightens when I turn it, it just remains loose the whole time, but I can't see any obvious reason why this should be the case. I'm hoping this can be fixed fairly easily, although I confess to not being very practically/mechanically minded so I thought I would ask for some advice on here.

Thanks,
Jonathan

There's a Manfrotto spares store in UK.

http://www.manfrottospares.com/

I ordered from them a quick plate for a MVH500AH and a retaining screw I had damaged and everything arrived to Spain in 24 hours, free shipping even.