Darrel,
You are right, the code I posted did not have the comparators turned off. I had noticed that and thought that mistake was fixed. It is now, thanks for catching it.
That unfortunetly did not correct the problem.

VREF+ and VREF- are both now set to external pins, I have tried it with VREF- set to VDD. VREF- is set to ground. For all practical purposes the same, but it was thought using a dedicated pin for VREF- was worth a try.