IIS 8.5 Server Down Event ID 5139

[masterinterface]

Hi there.

On Windows Server 2012 64x IIS 8.5

After completing the steps exactly as specified for IIS in: https://www.cloudflare.com/resources-downloads/

(this included registering the module with the install script and modifying the ini file as specified)

IIS is now down: (serving http 503 on all websites) - all application pools are shut down because of repeated Event ID 5139 happening.

I have removed the module through the IIS manager UI. But the problem still persists.

Please could I get info on what could be causing the issue, and how to get the pools up and running correctly as they were before.

Urgent help needed, very appreciated.

EDIT: IIS pools and sites back up and running ok after removing the c:HttpModules\FSXFFHttpModule.dll line from applicationHost file under C:\Windows\System32\inetsrv\config

How can I use the module without making the pools crash because of Event ID 5139?

EDIT 2: In relation to config file instructions that require changing "X-Forwarded-For to CF-Connecting-IP.":

I've noticed that cloudflare sends in the HTTP header with HTTP_CF_CONNECTING_IP (and not CF-Connecting-IP). Could this be in any way realted the issue?