When I changed PC's I just installed ADE and when it started up the wizard asked me to authorize which I did with my old email address and old password.
I've got the same problem. I'm getting an error: "You can only authorize this computer with an Adobe ID that hasn't been previously used to authorize any other computer or mobile device. Please try again".
I've already deauthorised my other computer now, but still I'm getting the same error.
If I wasn't convinced before that DRM is a load of rubbish, I certainly am now. Is there any other way around this?