If I recall correctly, I think people got that prompt about "already being associated with an account" if they bought the CD, but used the code to get and install the download version at some point, and then later tried to install from the CD. Getting the download somehow obligated one to the download version and linked all of it together so that people couldn't use both. At least that's the way I sorta remember it. It produced a lot of complaints, and whether that will still happen this year or not, I don't know.
