This error message usually occurs, when .NET Framework 3.5 couldn't loaded correctly. You'll have to activate .NET Framework 3.5 in Windows 8 / Windows 8.1. .NET Framework is usually installed by default, but needs to be activated additionally. Here's a guide on how-to:
Open the Control Panel -> Programs and Features and activate .NET Framework 3.5. Windows will download the installation files and reboot automatically.
It's important to re-install the Password Manager afterwards, in order to register the components with the .NET Framework.