[Paraview] Suddenly cannot volume render?

[Robert.Atwood at diamond.ac.uk]

Hi
Paraview on my desktop (windows 7 64 bits ) is refusing to volume-render, I am sure exactly the same sequence of commands gave me some images the other day. What configuration of the system could result in only 'outline' when 'volume' is selected?? Other displays (point, wireframe, surfeac, slice) all work as expected but 'volume' results in an empty outline cube.
Any thoughts? 
Thanks
Robert


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