Repaired SU. No luck. Uninstalled then reinstalled SU. No luck.
After doing some experimenting it appears I've hit a limitation of the 'Proper Animation' (PA) plugin.
When PA disabled SU only produces a still image for each scene and there is no animation from scene to scene i.e. the same as exported animation. PA appears not to support exporting animations. Since I am moving an object and not changing the camera angle/view I understand this is to be expected of SU.
I have got round the problem by using Camstudio to generate avi & swf files of the animation
Thanks for the responses & help.
Nick