Little Green Button Help Centre

Little Green Button requires the installation of Microsoft .NET Framework 3.5. If this is not already installed, do the following in Windows to enable it.

Navigate to Control Panel\Programs\Programs and Features
Click Turn Windows Features on.
 Click .NET Framework 3.5 (includes .NET 2.0 and 3.0)

The following article also contains information to help you install it:

 https://blogs.technet.microsoft.com/mniehaus/2015/08/31/adding-features-including-net-3-5-to-windows-10/