Unable to access ASP.NET Settings of a domain in Plesk: Can’t detect .NET version. Possible site does not use ASP.NET

Symptoms

• Plesk Obsidian running on a Windows server

• The error message

  aspnetcfg failed: Can't detect .NET version. Possible site does not use ASP.NET (Error code 1)

  

  is displayed in the Plesk GUI when:

  - opening ASP.NET settings in Plesk at Domains > example.com > ASP.NET Settings.

  - changing password of the main FTP user at Domains > example.com > FTP Access

  - issuing a Let's Encrypt certificate for a domain.

  - attempting to open the page Domains > example.com > Hosting & DNS > Hosting
  

• The affected website may also load with the following error message:

  The page cannot be displayed because an external server error has occurred.

Cause

Misconfiguration in IIS, during which both of the following settings are in place when checked:

• .NET CLR version is set to No Managed Code in application pool settings of the website in IIS Manager > HOSTNAME > Application Pools > example.com.
• Microsoft ASP.NET support is enabled in Plesk at Domains > example.com > Hosting & DNS > Hosting

Resolution

In order to resolve the IIS configuration issues, you should do the following:

1. Log into Plesk

2. Go to Domains > example.com > Hosting & DNS > Hosting
   

   Note: If the Hosting tab is inaccessible, do the following to make it accessible:

   1. Connect to the server via RDP
   2. Go to IIS > HOSTNAME > Application Pools > example.com > double click on domain and switch the .NET CLR version from No Managed Code to .NET CLR v4
      

    

3. Disable the option Microsoft ASP.NET support and click Apply.

4. Enable the option Microsoft ASP.NET support back and click Apply.