[Plugin: Image Store] No Thumnails

When I create a new gallery and try to upload images I get no thumbnails.

Can anyone help?
I notice the script doesn’t create a _resized folder – but does when I scan the folder – so I don’t think it is a permissions problem and have changed permissions on server.

I get no error messages either.

http://wordpress.org/extend/plugins/image-store/