Turns out it was NuGet that was corrupt. Uninstalled. Reinstalled and blammo back in business.
There have been joys too great to be described in words, and there have been griefs upon which I have not dared to dwell, and with these in mind I say, climb if you will, but remember that courage and strength are naught without prudence, and that a momentary negligence may destroy the happiness of a lifetime. Do nothing in haste, look well to each step, and from the beginning think what may be the end. - Edward Whymper Climb On!