We use version 2.0 of the .NET Framework in order to ensure compatibility with older versions of Windows. In theory subsequent versions are backwardly compatible, but it seems that Microsoft have changed the rules again with Windows 8.1 (we have many users on Windows 8 with no problems). That said there does appear to be a solution. Click here for Microsoft web page explaining this.
The relevant section is also stated here: You can also enable the .NET Framework 3.5 yourself through Control Panel. In Control Panel, choose Programs and Features, choose Turn Windows features on or off, and then select the .NET Framework 3.5 (includes .NET 2.0 and 3.0) check box. This option requires an Internet connection. You do not need to select the child items for Windows Communication Foundation (WCF) HTTP activation unless you are a developer who requires WCF script and handler mapping functionality. Turning Windows features on or off in Control Panel.
