If you're using Vista or higher, the .NET Framework version that DisplayFusion targets is built-in to Windows. There are a few things you can do to try and repair it:

• Run the following at a command prompt: sfc /scannow
• Check for Windows Updates, and install any .NET Framework updates available
• Remove and re-add the .NET Framework in Programs and Features > Turn Windows features on or off

If you still have any trouble after trying the above, please let me know.

Thanks!