IIS 8.5 Server Down Event ID 5139

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?

Start with the IIS installation instructions at the linked Cloudflare resource and the module registration steps, then inspect the applicationHost configuration and the c:\HttpModules\FSXFFHttpModule.dll entry. Compare the Event ID 5139 failure with the HTTP_CF_CONNECTING_IP header noted in the report. Done would mean identifying the cause and documenting a configuration that keeps the application pools running.

Written by the indexing model from the issue text.