>Yes Brian, the center sensor is soft but either side is >sharp in the same focal plane. I have already ruled out >back/front focus.
I'm still not clear on exactly what is happening.
You seem to be saying that you focused on a subject using the centre AF point, the part of the subject under that AF point is soft, but parts of the subject - that are at the same distance - either side of the centre are sharp. That's confusing...
So let's see some example images - one from the half that are wrong and one from the half that are right would be a good start - and more details of the settings.