The text below is my boilerplate for an invalid key message, but your message sounds like you may not have this problem. Is the copy of OneCare you are trying to activate an install from the CD or is it a download? The error you are getting would happen if you have downloaded the beta of OneCare from the Connect web site and are trying to activate it with a retail key. If this is a CD install or an install from http://onecare.live.com and the retail key is returning the above error, see the text below and contact support to have the problem investigated if you can confirm that the key is indeed correct.
If you are getting an error about the key being invalid, you are mistaking at least one character or you have a misprinted key. The latter is very rare, though it can happen.
I hate the font that they use for the key - some characters are miserable to discern. J and I look all too much alike, as do O and 0.
I recommend that you use a magnifying glass to check the characters closely - I find that I need to do this. If you are still encountering a problem with activation, you have about 2 weeks to get activated, so I'd go ahead and open an email request to support, explaining the problem. See the FAQ and use the Trial user option to start the email request. If you can provide a digital image - scan or photo - of the key to the tech that responds, they can validate the key for you.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
