Patrick,
I think that I can put the issue down to the version 17.0.9.1 drivers that were downloaded by VAIO Update and, like a dutiful user, I applied. I reinstalled the original Win 8 version 16 drivers, reset the power setting on balanced plan to default and waited to see what happened.
Nothing, i.e. no crashes. Floats in an out of sleep like it should.
Problem solved.
Thanks again for all the help.
Tony
