[Plugin: GD Star Rating] Visitors' votes not registering & showing

I love the visuals of this plugin. It’s exactly what I wanted.

My problem is it will register my (author’s) vote but others’ votes don’t seem to register.

Some visitors say it seems to work – as in, they hover and the stars fill in and they select and the stars turn solid. Others say it won’t select and go solid.

This is definitely the most feature / menu laden plugin I have on my site so it may well be that I have not ticked a box or something but I can’t see it.

Any help much appreciated.

http://wordpress.org/extend/plugins/gd-star-rating/