Open OneCare and click Help/About...
The subscription ID shown is the LiveID that you must enter when you try to make the PC a hub (or perform any other task that requires you to login/confirm your credentials).
If you are using the LiveID and it is not letting you proceed, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator