Minimum requirement: WindowsXP or later and .NET Framework 4.0

You need to install .NET Framework 4.0 .

.NET Framework download site

• Requirement: Microsoft .NET Framework 4(Web Installer)
• English Download here : Microsoft .NET Framework 4(Web Installer)

Others

• Tween uses Win32 API, so doesn't work on Mono.
• Tween works on Windows7, but it depends on its configuration.