Note: This article covers a legacy version of Little Green Button. Please strive to always run the latest version of the software.
The 3.6 and earlier versions of Little Green Button require the installation of Microsoft .NET Framework 3.5. If this is not already installed, do the following in Windows to enable it.
Navigate to Settings
Open the 'Apps' section.
Click 'Programs and Features' towards the bottom of this section.
On the left hand side of this window, click 'Turn Windows features on or off'
Enable .NET Framework 3.5 (includes .NET 2.0 and 3.0)
You can get to this window quicker by running the 'optionalfeatures.exe' command.
Explicit troubleshooting regarding installing this is outside the scope of this article, but you can find more information on the Microsoft Docs.