I don't know what your specific problem is. However, you've clearly not read the forums if you think nobody else is reading them. Have you contacted support and not gotten an email response?
It sounds like you have activated a OneCare subscription if the key code is reported to be in use when you try to activate your installed copy. Is this a reinstall or did OneCare never update to subscribed status after you initially activated.
If you have an active subscription, which is what was created when you activated originally, you need to use the same LiveID on the subsequent activations. You can't use the same key twice. If you are arriving at a screen to purchase or provide a token, you are likely not using the same LiveID as the subscription ID.
If this is a install to a 2nd PC, on the first PC, open OneCare and click Help and then About to see your Subscription ID. That is the LiveID to sign in with.
If you don't recall the LiveID you used for your subscription, and this is a reinstall, you will need to contact support who can provide that information to you using your Key and/or contact information.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
Alternatively, sign in at http://billing.microsoft.com with email addresses that you have set up as LiveIDs and one will show your subscription listed - that would the LiveID to use to activate with.
If you have an active subscription as shown at http://billing.microsoft.com and this is your first installation, but OneCare has not updated your activation status, please contact support.
-steve
