---
title: "Fixing \"Class not registered\" error in Sage CRM .NET pages — Ivan Kahl"
description: "A July 2018 Windows update can break Sage CRM .NET pages with a \"Class not registered\" error. A small IIS authentication change resolves it."
url: https://ivankahl.com/blog/fixing-class-not-registered-error-in-sage-crm-net-pages/
published: 2018-08-01T00:00:00.000Z
tags:
  - "Sage CRM"
  - ".NET"
  - "IIS"
  - "Windows Update"
  - "Windows"
---

01 Aug 2018 · 1 min read

# Fixing "Class not registered" error in Sage CRM .NET pages

A July 2018 Windows update can break Sage CRM .NET pages with a "Class not registered" error. A small IIS authentication change resolves it.

You might have been unfortunate enough to have run into this obscure error in a Sage CRM instance:

![The dreaded ](https://ivankahl.netlify.com/static/crm_error-8c52876791d573932be449e32f7f47ed-6444b.png)

According to the Sage CRM forum, this error is caused by an update for Windows released in July 2018 (more specifically the update [KB4338420](https://support.microsoft.com/en-us/help/4338420/description-of-the-security-and-quality-rollup-updates-for-net-framewo)). This issue has not only caused errors in Sage CRM, but also other IIS applications.

## Solution

This solution was provided by Jeff Richards in this forum post from [here](https://community.sagecrm.com/user_community/f/84/p/14369/39491.aspx#). I am posting it as a reference for myself and others who may run into this issue.

The following steps should configure IIS to not cause any further issues such as this:

1.  Open IIS Manager and navigate to the CRM site:  
    ![IIS\_CRM-bb99e6db7420b056176c93a5b4eb9906-cd5f0](https://blog.ivankahl.com/content/images/2019/02/IIS_CRM-bb99e6db7420b056176c93a5b4eb9906-cd5f0.png)
2.  Go to **Authentication**:  
    ![IIS\_Authentication-d0fd204d7da38abd1e8b532e8e612a72-d741b](https://blog.ivankahl.com/content/images/2019/02/IIS_Authentication-d0fd204d7da38abd1e8b532e8e612a72-d741b.png)
3.  Select the *Anonymous Authentication*, click **Edit…** on the right, select the *Application pool identity* radio button and click **OK** to save the changes.  
    ![IIS\_ChangeSiteIdentity-7e1c9893aa6e0cc369270c10c9fbb8af-52fd6](https://blog.ivankahl.com/content/images/2019/02/IIS_ChangeSiteIdentity-7e1c9893aa6e0cc369270c10c9fbb8af-52fd6.png)
4.  You may need to restart the CRM website for the changes to take effect:  
    ![IIS\_Restart-81dc76a79aebfa70778a3728706c9d8d-7df5b](https://blog.ivankahl.com/content/images/2019/02/IIS_Restart-81dc76a79aebfa70778a3728706c9d8d-7df5b.png)

## Conclusion

This should be enough to resolve the issue according to the Sage CRM forum. I can confirm that this solution worked for me at one of my client’s sites after much troubleshooting. If you still have issues, let me know in the comments and we’ll see if we can find another solution.

Tags: [Sage CRM](https://ivankahl.com/blog/tags/sage-crm/), [.NET](https://ivankahl.com/blog/tags/dotnet/), [IIS](https://ivankahl.com/blog/tags/iis/), [Windows Update](https://ivankahl.com/blog/tags/windows-update/), [Windows](https://ivankahl.com/blog/tags/windows/)