• "When AirFader starts, I only see white boxes with a red diagonal crisscross"
• I get error "System.IO.FileNotFoundException..." when starting AirFader

These errors simply means you need to install Microsoft .NET Framework version 2, 3 or 3.5. (Newer versions of windows do not require this.)

Microsoft .NET Framework 3.5 is available for free here:

http://www.microsoft.com/download/en/details.aspx?id=22

Once that's installed, it should resolve this issue.