I don't think that anyone did much more than notice that 4.0 was not being installed on XP machines. We all downloaded .NET Framework 4.0 from Microsoft directly and installed it, but it didn't make a difference for most. I am sure that you are the first to raise the issue of what version of .NET that AC version 6 is trying to use. And also went the extra step of getting AC tech support involved.
Let us know if it helps to uninstall earlier versions of .NET, if you take that step.
