New install stuck on splash screen at User Initialize

I have a very frustrating issue.

I upgraded a 15.3 install to 2017.2 and then got the Issue where it gets stuck at the splash screen at Initialising User.

I then uninstalled everything, removed all visible traces (App pools, Sites and folders) of the Xtraction install.

Re-installed with a blank DB and the Datamodel that comes with the install.

The issue persists. I cannot get the install to work again.

No info is written to the logs, but running in bebug mode = true gives me the following.

(mx.messaging.messages::ErrorMessage)#0

  body = (null)

  clientId = "b7e8c0ff-c281-4df8-b2fc-2d366ee2be64"

  correlationId = "7B457FC7-32FB-8ABF-DD33-3C6F2DC15252"

  destination = "fluorine"

  extendedData = (Object)#1

  faultCode = "Server.Processing"

  faultDetail = (null)

  faultString = "Object reference not set to an instance of an object."

  headers = (Object)#2

    DSId = "126250c6996249bb86605bb981bf5cdf"

  messageId = "7bfb3655-57d7-4d7d-8fa1-0163aed15ef4"

  rootCause = (null)

  timestamp = 203985828

  timeToLive = 0