Thanks for your reply.
I seem to have fixed the problem by disabling MouseImp.
Interestingly my other machine that I run SolidWorks on doesn't have an issue with MouseImp.
It's no bit deal though, because it's only my laptop that I'll be using when I'm away.
I'm even surprised that SW and SpaceNavigator run reasonably well on a low end laptop with Intel intergrated graphics.
The SpaceNavigator seems a solid quality unit delivered in a few days from 3DConnexions site half way around the world.
I appreciate your prompt response.